diff --git a/codex-rs/core/src/compact.rs b/codex-rs/core/src/compact.rs
index 4dbbd3a424..3ddbea4463 100644
--- a/codex-rs/core/src/compact.rs
+++ b/codex-rs/core/src/compact.rs
@@ -155,7 +155,7 @@ pub(crate) async fn run_compact_task(
         trace_id: turn_context.trace_id.clone(),
         started_at: turn_context.turn_timing_state.started_at_unix_secs().await,
         model_context_window: turn_context.model_context_window(),
-        collaboration_mode_kind: turn_context.mode,
+        collaboration_mode_kind: turn_context.mode(),
     });
     sess.send_event(&turn_context, start_event).await;
     run_compact_task_inner(
@@ -257,7 +257,7 @@ async fn run_compact_task_inner_impl(
     let mut history = sess.clone_history().await;
     history.record_items(
         &[initial_input_for_turn.into()],
-        turn_context.model_info.truncation_policy.into(),
+        turn_context.model_info().truncation_policy.into(),
     );
 
     let max_retries = turn_context.provider.info().stream_max_retries();
@@ -277,7 +277,7 @@ async fn run_compact_task_inner_impl(
         // Clone is required because of the loop
         let turn_input = history
             .clone()
-            .for_prompt(&turn_context.model_info.input_modalities);
+            .for_prompt(&turn_context.model_info().input_modalities);
         let turn_input_len = turn_input.len();
         let prompt = Prompt {
             input: turn_input,
@@ -742,10 +742,10 @@ async fn drain_to_completed(
     let mut stream = client_session
         .stream(
             prompt,
-            &turn_context.model_info,
+            turn_context.model_info(),
             &turn_context.session_telemetry,
-            turn_context.reasoning_effort.clone(),
-            turn_context.reasoning_summary,
+            turn_context.reasoning_effort().cloned(),
+            turn_context.reasoning_summary(),
             turn_context.config.service_tier.clone(),
             responses_metadata,
             // Rollout tracing currently models remote compaction only; local compaction streams
diff --git a/codex-rs/core/src/compact_remote.rs b/codex-rs/core/src/compact_remote.rs
index eb686725c9..932993d14c 100644
--- a/codex-rs/core/src/compact_remote.rs
+++ b/codex-rs/core/src/compact_remote.rs
@@ -90,7 +90,7 @@ pub(crate) async fn run_remote_compact_task(
         trace_id: turn_context.trace_id.clone(),
         started_at: turn_context.turn_timing_state.started_at_unix_secs().await,
         model_context_window: turn_context.model_context_window(),
-        collaboration_mode_kind: turn_context.mode,
+        collaboration_mode_kind: turn_context.mode(),
     });
     sess.send_event(&turn_context, start_event).await;
 
@@ -206,7 +206,7 @@ async fn run_remote_compact_task_inner_impl(
     let compaction_trace = sess.services.rollout_thread_trace.compaction_trace_context(
         turn_context.sub_id.as_str(),
         compaction_id.as_str(),
-        turn_context.model_info.slug.as_str(),
+        turn_context.model_info().slug.as_str(),
         turn_context.provider.info().name.as_str(),
     );
     let compaction_item = TurnItem::ContextCompaction(context_compaction_item);
@@ -235,7 +235,7 @@ async fn run_remote_compact_task_inner_impl(
                 sess.services.rollout_thread_trace.compaction_trace_context(
                     fallback_turn_context.sub_id.as_str(),
                     compaction_id.as_str(),
-                    fallback_turn_context.model_info.slug.as_str(),
+                    fallback_turn_context.model_info().slug.as_str(),
                     fallback_turn_context.provider.info().name.as_str(),
                 );
             let fallback_result = run_remote_compact_attempt(
@@ -249,8 +249,8 @@ async fn run_remote_compact_task_inner_impl(
             .await;
             record_model_fallback(
                 &sess.services.session_telemetry,
-                turn_context.model_info.slug.as_str(),
-                fallback_turn_context.model_info.slug.as_str(),
+                turn_context.model_info().slug.as_str(),
+                fallback_turn_context.model_info().slug.as_str(),
                 compaction_metadata.reason(),
                 compaction_metadata.implementation(),
                 fallback_result.as_ref().err(),
diff --git a/codex-rs/core/src/compact_remote_request.rs b/codex-rs/core/src/compact_remote_request.rs
index 8a46e6ce18..9ca0b88392 100644
--- a/codex-rs/core/src/compact_remote_request.rs
+++ b/codex-rs/core/src/compact_remote_request.rs
@@ -58,7 +58,7 @@ pub(super) async fn run_remote_compact_attempt(
     let trace_input_history = compaction_trace
         .is_enabled()
         .then(|| history.raw_items().cloned().collect());
-    let prompt_input = history.for_prompt(&turn_context.model_info.input_modalities);
+    let prompt_input = history.for_prompt(&turn_context.model_info().input_modalities);
     let tool_router = &step_context.tool_router;
     let prompt = Prompt {
         input: prompt_input,
@@ -79,11 +79,11 @@ pub(super) async fn run_remote_compact_attempt(
         .model_client
         .compact_conversation_history(
             &prompt,
-            &turn_context.model_info,
+            turn_context.model_info(),
             turn_state,
             CompactConversationRequestSettings {
-                effort: turn_context.reasoning_effort.clone(),
-                summary: turn_context.reasoning_summary,
+                effort: turn_context.reasoning_effort().cloned(),
+                summary: turn_context.reasoning_summary(),
                 service_tier: if sess.services.auth_manager.auth_mode() == Some(AuthMode::ApiKey) {
                     None
                 } else {
diff --git a/codex-rs/core/src/compact_remote_v2.rs b/codex-rs/core/src/compact_remote_v2.rs
index b7cebf0b4d..198c469f1c 100644
--- a/codex-rs/core/src/compact_remote_v2.rs
+++ b/codex-rs/core/src/compact_remote_v2.rs
@@ -118,7 +118,7 @@ pub(crate) async fn run_remote_compact_task(
         trace_id: turn_context.trace_id.clone(),
         started_at: turn_context.turn_timing_state.started_at_unix_secs().await,
         model_context_window: turn_context.model_context_window(),
-        collaboration_mode_kind: turn_context.mode,
+        collaboration_mode_kind: turn_context.mode(),
     });
     sess.send_event(&turn_context, start_event).await;
 
@@ -234,7 +234,7 @@ async fn run_remote_compact_task_inner_impl(
     let compaction_trace = sess.services.rollout_thread_trace.compaction_trace_context(
         turn_context.sub_id.as_str(),
         compaction_id.as_str(),
-        turn_context.model_info.slug.as_str(),
+        turn_context.model_info().slug.as_str(),
         turn_context.provider.info().name.as_str(),
     );
     let compaction_item = TurnItem::ContextCompaction(context_compaction_item);
@@ -264,7 +264,7 @@ async fn run_remote_compact_task_inner_impl(
                 sess.services.rollout_thread_trace.compaction_trace_context(
                     fallback_turn_context.sub_id.as_str(),
                     compaction_id.as_str(),
-                    fallback_turn_context.model_info.slug.as_str(),
+                    fallback_turn_context.model_info().slug.as_str(),
                     fallback_turn_context.provider.info().name.as_str(),
                 );
             let fallback_result = run_remote_compact_v2_attempt(
@@ -278,8 +278,8 @@ async fn run_remote_compact_task_inner_impl(
             .await;
             record_model_fallback(
                 &sess.services.session_telemetry,
-                turn_context.model_info.slug.as_str(),
-                fallback_turn_context.model_info.slug.as_str(),
+                turn_context.model_info().slug.as_str(),
+                fallback_turn_context.model_info().slug.as_str(),
                 compaction_metadata.reason(),
                 compaction_metadata.implementation(),
                 fallback_result.as_ref().err(),
@@ -380,10 +380,10 @@ async fn run_remote_compaction_request_v2(
         let result = match client_session
             .stream(
                 prompt,
-                &turn_context.model_info,
+                turn_context.model_info(),
                 &turn_context.session_telemetry,
-                turn_context.reasoning_effort.clone(),
-                turn_context.reasoning_summary,
+                turn_context.reasoning_effort().cloned(),
+                turn_context.reasoning_summary(),
                 turn_context.config.service_tier.clone(),
                 responses_metadata,
                 &InferenceTraceContext::disabled(),
diff --git a/codex-rs/core/src/compact_remote_v2_attempt.rs b/codex-rs/core/src/compact_remote_v2_attempt.rs
index 6b567801b1..029b821901 100644
--- a/codex-rs/core/src/compact_remote_v2_attempt.rs
+++ b/codex-rs/core/src/compact_remote_v2_attempt.rs
@@ -69,7 +69,7 @@ pub(super) async fn run_remote_compact_v2_attempt(
         .is_enabled()
         .then(|| history.raw_items().cloned().collect());
     let (mut input, prompt_input_metadata): (Vec<_>, Vec<_>) = history
-        .for_prompt_annotated(&turn_context.model_info.input_modalities)
+        .for_prompt_annotated(&turn_context.model_info().input_modalities)
         .into_iter()
         .map(|envelope| (envelope.item, envelope.metadata))
         .unzip();
@@ -91,7 +91,7 @@ pub(super) async fn run_remote_compact_v2_attempt(
         )
         .await;
     let trace_attempt = compaction_trace.start_attempt(&serde_json::json!({
-        "model": turn_context.model_info.slug.as_str(),
+        "model": turn_context.model_info().slug.as_str(),
         "instructions": prompt.base_instructions.text.as_str(),
         "input": &prompt.input,
         "parallel_tool_calls": prompt.parallel_tool_calls,
diff --git a/codex-rs/core/src/compact_token_budget.rs b/codex-rs/core/src/compact_token_budget.rs
index 2abb6b0b24..60d25c53d8 100644
--- a/codex-rs/core/src/compact_token_budget.rs
+++ b/codex-rs/core/src/compact_token_budget.rs
@@ -32,7 +32,7 @@ pub(crate) async fn run_manual_compact_task(
         trace_id: turn_context.trace_id.clone(),
         started_at: turn_context.turn_timing_state.started_at_unix_secs().await,
         model_context_window: turn_context.model_context_window(),
-        collaboration_mode_kind: turn_context.mode,
+        collaboration_mode_kind: turn_context.mode(),
     });
     sess.send_event(&turn_context, start_event).await;
 
diff --git a/codex-rs/core/src/context/node_repl_review_evidence.rs b/codex-rs/core/src/context/node_repl_review_evidence.rs
index cdd7942350..5d5dbae543 100644
--- a/codex-rs/core/src/context/node_repl_review_evidence.rs
+++ b/codex-rs/core/src/context/node_repl_review_evidence.rs
@@ -31,7 +31,7 @@ pub(crate) enum NodeReplReviewEvidenceMode {
 
 pub(crate) fn node_repl_review_evidence_mode(turn: &TurnContext) -> NodeReplReviewEvidenceMode {
     let features = &turn.config.features;
-    if turn.model_info.node_repl_auto_review_required
+    if turn.model_info().node_repl_auto_review_required
         || features.enabled(Feature::GuardianEnhancedNodeReplTranscripts)
             && features.enabled(Feature::GuardianNodeReplTranscriptImages)
     {
diff --git a/codex-rs/core/src/context_manager/history.rs b/codex-rs/core/src/context_manager/history.rs
index 94ee21ae96..2d9b647321 100644
--- a/codex-rs/core/src/context_manager/history.rs
+++ b/codex-rs/core/src/context_manager/history.rs
@@ -254,8 +254,10 @@ impl ContextManager {
     // Estimate token usage using byte-based heuristics from the truncation helpers.
     // This is a coarse lower bound, not a tokenizer-accurate count.
     pub(crate) fn estimate_token_count(&self, turn_context: &TurnContext) -> Option<i64> {
-        let model_info = &turn_context.model_info;
-        let personality = turn_context.personality.or(turn_context.config.personality);
+        let model_info = &turn_context.model_info();
+        let personality = turn_context
+            .personality()
+            .or(turn_context.config.personality);
         let base_instructions = BaseInstructions {
             text: model_info.get_model_instructions(personality),
             provenance: None,
diff --git a/codex-rs/core/src/guardian/review.rs b/codex-rs/core/src/guardian/review.rs
index 943bd22509..145fa12dcb 100644
--- a/codex-rs/core/src/guardian/review.rs
+++ b/codex-rs/core/src/guardian/review.rs
@@ -249,7 +249,7 @@ async fn record_guardian_non_denial(session: &Arc<Session>, turn_id: &str) {
 }
 
 async fn record_guardian_denial(session: &Arc<Session>, turn: &Arc<TurnContext>, turn_id: &str) {
-    let policy = if turn.model_info.model_specialty.as_deref() == Some(MODEL_SPECIALTY_CYBER) {
+    let policy = if turn.model_info().model_specialty.as_deref() == Some(MODEL_SPECIALTY_CYBER) {
         GuardianRejectionCircuitBreakerPolicy::CyberModel
     } else {
         GuardianRejectionCircuitBreakerPolicy::Standard
@@ -335,7 +335,7 @@ async fn run_guardian_review(
         .config
         .config_layer_stack
         .requirements()
-        .auto_review_required_for_model(&turn.model_info.slug)
+        .auto_review_required_for_model(&turn.model_info().slug)
         || turn.config.features.enabled(Feature::GuardianV2))
         && !requires_synchronous_review
         && options
@@ -722,7 +722,7 @@ async fn run_guardian_review(
             assessment.rationale.trim()
         };
         let rejection_instructions = turn
-            .model_info
+            .model_info()
             .model_messages
             .as_ref()
             .and_then(|messages| messages.auto_review.as_ref())
@@ -847,7 +847,7 @@ pub(super) async fn guardian_review_session_config(
             fallback
         }
     };
-    let model_override = turn.model_info.auto_review_model_override.as_deref();
+    let model_override = turn.model_info().auto_review_model_override.as_deref();
     let review_model_id = model_override.unwrap_or(default_review_model_id);
     let review_model = available_models
         .iter()
@@ -868,17 +868,17 @@ pub(super) async fn guardian_review_session_config(
         (review_model_id.to_string(), reasoning_effort)
     } else {
         let reasoning_effort = preferred_reasoning_effort(
-            turn.model_info
+            turn.model_info()
                 .supported_reasoning_levels
                 .iter()
                 .any(|preset| preset.effort == codex_protocol::openai_models::ReasoningEffort::Low),
-            turn.reasoning_effort
-                .clone()
-                .or_else(|| turn.model_info.default_reasoning_level.clone()),
+            turn.reasoning_effort()
+                .or(turn.model_info().default_reasoning_level.as_ref())
+                .cloned(),
         );
         (
             model_override
-                .unwrap_or(turn.model_info.slug.as_str())
+                .unwrap_or(turn.model_info().slug.as_str())
                 .to_string(),
             reasoning_effort,
         )
@@ -899,7 +899,7 @@ pub(super) async fn guardian_review_session_config(
         guardian_reasoning_effort.clone(),
         guardian_model_info.model_messages.as_ref(),
     )?;
-    if turn.model_info.node_repl_auto_review_required {
+    if turn.model_info().node_repl_auto_review_required {
         spawn_config
             .features
             .enable(Feature::RetainClientDeveloperMessages)
@@ -909,7 +909,7 @@ pub(super) async fn guardian_review_session_config(
                 )
             })?;
     }
-    if guardian_model != turn.model_info.slug {
+    if guardian_model != turn.model_info().slug {
         spawn_config.model_context_window = None;
         spawn_config.model_auto_compact_token_limit = None;
     }
@@ -974,8 +974,8 @@ async fn run_guardian_review_session_before_deadline(
                 guardian_catalog_contains_auto_review: session_config.catalog_contains_auto_review,
                 guardian_review_model_overridden: session_config.model_overridden,
                 guardian_review_model_override: session_config.model_override,
-                reasoning_summary: turn.reasoning_summary,
-                personality: turn.personality,
+                reasoning_summary: turn.reasoning_summary(),
+                personality: turn.personality(),
                 external_cancel,
                 deadline,
             }),
diff --git a/codex-rs/core/src/guardian/review_session.rs b/codex-rs/core/src/guardian/review_session.rs
index 563381973a..3f29a2595e 100644
--- a/codex-rs/core/src/guardian/review_session.rs
+++ b/codex-rs/core/src/guardian/review_session.rs
@@ -438,7 +438,7 @@ impl GuardianReviewSessionManager {
             .with_node_repl_policy_eligibility(
                 parent_context
                     .turn()
-                    .model_info
+                    .model_info()
                     .node_repl_auto_review_required,
             );
             let spawn_cancel_token = self.cancellation_token.child_token();
@@ -528,7 +528,7 @@ impl GuardianReviewSessionManager {
             params
                 .parent_context
                 .turn()
-                .model_info
+                .model_info()
                 .node_repl_auto_review_required,
         );
         let mut spawned_trunk = false;
@@ -952,7 +952,7 @@ async fn run_review_on_session(
                 .sync_session_approved_hosts_to(&review_session.session.services.network_approval)
                 .await;
 
-            if params.parent_context.turn().model_info.node_repl_auto_review_required
+            if params.parent_context.turn().model_info().node_repl_auto_review_required
                 && matches!(
                     &params.request,
                     GuardianApprovalRequest::McpToolCall { server, tool_name, .. }
@@ -1607,10 +1607,10 @@ mod tests {
 
     async fn test_review_params() -> GuardianReviewSessionParams {
         let (session, turn) = crate::session::tests::make_session_and_context().await;
-        let model = turn.model_info.slug.clone();
-        let reasoning_effort = turn.reasoning_effort.clone();
-        let reasoning_summary = turn.reasoning_summary;
-        let personality = turn.personality;
+        let model = turn.model_info().slug.clone();
+        let reasoning_effort = turn.reasoning_effort().cloned();
+        let reasoning_summary = turn.reasoning_summary();
+        let personality = turn.personality();
         #[allow(deprecated)]
         let cwd = turn.cwd.clone();
         let spawn_config = build_guardian_review_session_config(
diff --git a/codex-rs/core/src/guardian/tests.rs b/codex-rs/core/src/guardian/tests.rs
index eb9d452398..908ec42807 100644
--- a/codex-rs/core/src/guardian/tests.rs
+++ b/codex-rs/core/src/guardian/tests.rs
@@ -14,6 +14,7 @@ use crate::guardian::prompt::guardian_policy_prompt_with_config_and_template;
 use crate::guardian::review::guardian_review_session_config;
 use crate::guardian::review::routes_approval_to_guardian_with_reviewer;
 use crate::session::session::Session;
+use crate::session::tests::update_turn_settings_for_test;
 use crate::session::turn_context::TurnContext;
 use crate::test_support;
 use codex_analytics::GuardianApprovalRequestSource;
@@ -1185,12 +1186,10 @@ async fn build_guardian_prompt_items_keeps_required_node_repl_reviews_generic()
 {
     let (session, mut turn) =
         guardian_test_session_and_turn_with_base_url("http://localhost").await;
-    Arc::make_mut(
-        &mut Arc::get_mut(&mut turn)
-            .expect("turn should be uniquely owned")
-            .model_info,
-    )
-    .node_repl_auto_review_required = true;
+    update_turn_settings_for_test(
+        Arc::get_mut(&mut turn).expect("turn should be uniquely owned"),
+        |settings| Arc::make_mut(&mut settings.model_info).node_repl_auto_review_required = true,
+    );
     seed_guardian_parent_history(&session, &turn).await;
     let context = GuardianReviewContext::from(&turn);
 
@@ -1810,7 +1809,7 @@ async fn guardian_request_model_for_auto_review(
     match catalog {
         GuardianTestCatalog::Bundled => {}
         GuardianTestCatalog::ParentOnly => {
-            let parent_model = turn.model_info.as_ref().clone();
+            let parent_model = turn.model_info().as_ref().clone();
             let auth_manager = Arc::clone(&session.services.auth_manager);
             let models_manager = StaticModelsManager::new(
                 Some(auth_manager),
@@ -1824,13 +1823,14 @@ async fn guardian_request_model_for_auto_review(
                 .models_manager = Arc::new(models_manager);
         }
     }
-    Arc::make_mut(
-        &mut Arc::get_mut(&mut turn)
-            .expect("turn should be unique")
-            .model_info,
-    )
-    .auto_review_model_override = auto_review_model_override;
-    let parent_model = turn.model_info.slug.clone();
+    update_turn_settings_for_test(
+        Arc::get_mut(&mut turn).expect("turn should be unique"),
+        |settings| {
+            Arc::make_mut(&mut settings.model_info).auto_review_model_override =
+                auto_review_model_override
+        },
+    );
+    let parent_model = turn.model_info().slug.clone();
     let preferred_model = turn.provider.approval_review_preferred_model().to_string();
     let parent_turn_id = turn.sub_id.clone();
     seed_guardian_parent_history(&session, &turn).await;
@@ -2055,8 +2055,10 @@ async fn guardian_review_request_layout_matches_model_visible_request_snapshot()
     session.services.skills_service.clear_cache();
     turn.config = Arc::clone(&config);
     turn.provider = create_model_provider(config.model_provider.clone(), turn.auth_manager.clone());
-    Arc::make_mut(&mut turn.model_info).auto_review_model_override =
-        Some("codex-auto-review".to_string());
+    update_turn_settings_for_test(&mut turn, |settings| {
+        Arc::make_mut(&mut settings.model_info).auto_review_model_override =
+            Some("codex-auto-review".to_string());
+    });
     let session = Arc::new(session);
     let turn = Arc::new(turn);
     seed_guardian_parent_history(&session, &turn).await;
@@ -2330,8 +2332,10 @@ async fn guardian_reuses_prompt_cache_key_and_appends_prior_reviews() -> anyhow:
         .enable(Feature::GuardianReuseParentCompaction)
         .expect("Guardian parent-compaction reuse should be configurable");
     let turn_mut = Arc::get_mut(&mut turn).expect("turn should be unique");
-    Arc::make_mut(&mut turn_mut.model_info).auto_review_model_override =
-        Some("codex-auto-review".to_string());
+    update_turn_settings_for_test(turn_mut, |settings| {
+        Arc::make_mut(&mut settings.model_info).auto_review_model_override =
+            Some("codex-auto-review".to_string());
+    });
     turn_mut.config = Arc::new(config);
     seed_guardian_parent_history(&session, &turn).await;
 
@@ -3542,7 +3546,7 @@ async fn guardian_review_session_config_clears_context_overrides_for_distinct_ef
 async fn guardian_review_session_config_preserves_context_overrides_for_same_effective_model() {
     let server = start_mock_server().await;
     let (mut session, mut turn) = guardian_test_session_and_turn(&server).await;
-    let parent_model = turn.model_info.as_ref().clone();
+    let parent_model = turn.model_info().as_ref().clone();
     let auth_manager = Arc::clone(&session.services.auth_manager);
     Arc::get_mut(&mut session)
         .expect("session should be unique")
diff --git a/codex-rs/core/src/hook_runtime.rs b/codex-rs/core/src/hook_runtime.rs
index d4a5ee04eb..95803e418f 100644
--- a/codex-rs/core/src/hook_runtime.rs
+++ b/codex-rs/core/src/hook_runtime.rs
@@ -145,7 +145,7 @@ pub(crate) async fn run_pending_session_start_hooks(
             #[allow(deprecated)]
             cwd: turn_context.cwd.clone(),
             transcript_path: sess.hook_transcript_path().await,
-            model: turn_context.model_info.slug.clone(),
+            model: turn_context.model_info().slug.clone(),
             permission_mode: hook_permission_mode(turn_context),
             target,
         };
@@ -187,7 +187,7 @@ pub(crate) async fn run_pre_tool_use_hooks(
         #[allow(deprecated)]
         cwd: turn_context.cwd.clone(),
         transcript_path: sess.hook_transcript_path().await,
-        model: turn_context.model_info.slug.clone(),
+        model: turn_context.model_info().slug.clone(),
         permission_mode: hook_permission_mode(turn_context),
         tool_name: tool_name.name().to_string(),
         matcher_aliases: tool_name.matcher_aliases().to_vec(),
@@ -248,7 +248,7 @@ pub(crate) async fn run_permission_request_hooks(
         #[allow(deprecated)]
         cwd: turn_context.cwd.to_path_buf(),
         transcript_path: sess.hook_transcript_path().await,
-        model: turn_context.model_info.slug.clone(),
+        model: turn_context.model_info().slug.clone(),
         permission_mode: hook_permission_mode(turn_context),
         tool_name: payload.tool_name.name().to_string(),
         matcher_aliases: payload.tool_name.matcher_aliases().to_vec(),
@@ -290,7 +290,7 @@ pub(crate) async fn run_post_tool_use_hooks(
         #[allow(deprecated)]
         cwd: turn_context.cwd.clone(),
         transcript_path: sess.hook_transcript_path().await,
-        model: turn_context.model_info.slug.clone(),
+        model: turn_context.model_info().slug.clone(),
         permission_mode: hook_permission_mode(turn_context),
         tool_name,
         matcher_aliases,
@@ -366,8 +366,8 @@ pub(crate) async fn run_turn_stop_hooks(
     let request_metadata = turn_context
         .turn_metadata_state
         .current_meta_value_for_mcp_request(McpTurnMetadataContext {
-            model: step_context.model_info.slug.as_str(),
-            reasoning_effort: step_context.reasoning_effort.clone(),
+            model: step_context.settings.model_info.slug.as_str(),
+            reasoning_effort: step_context.settings.reasoning_effort().cloned(),
         })
         .map(|turn_metadata| {
             serde_json::Map::from_iter([(
@@ -381,7 +381,7 @@ pub(crate) async fn run_turn_stop_hooks(
         #[allow(deprecated)]
         cwd: turn_context.cwd.clone(),
         transcript_path,
-        model: turn_context.model_info.slug.clone(),
+        model: turn_context.model_info().slug.clone(),
         permission_mode: hook_permission_mode(turn_context),
         request_metadata,
         stop_hook_active,
@@ -450,7 +450,7 @@ pub(crate) async fn run_turn_interrupt_hooks(sess: &Arc<Session>, turn_context:
         #[allow(deprecated)]
         cwd: turn_context.cwd.clone(),
         transcript_path: sess.hook_transcript_path().await,
-        model: turn_context.model_info.slug.clone(),
+        model: turn_context.model_info().slug.clone(),
         permission_mode: hook_permission_mode(turn_context),
     };
     if let Err(err) = sess.flush_rollout().await {
@@ -474,7 +474,7 @@ pub(crate) async fn run_pre_compact_hooks(
         #[allow(deprecated)]
         cwd: turn_context.cwd.clone(),
         transcript_path: sess.hook_transcript_path().await,
-        model: turn_context.model_info.slug.clone(),
+        model: turn_context.model_info().slug.clone(),
         trigger: compaction_trigger_label(trigger).to_string(),
     };
     let preview_runs = sess.hooks().preview_pre_compact(&request);
@@ -511,7 +511,7 @@ pub(crate) async fn run_post_compact_hooks(
         #[allow(deprecated)]
         cwd: turn_context.cwd.clone(),
         transcript_path: sess.hook_transcript_path().await,
-        model: turn_context.model_info.slug.clone(),
+        model: turn_context.model_info().slug.clone(),
         trigger: compaction_trigger_label(trigger).to_string(),
     };
     let preview_runs = sess.hooks().preview_post_compact(&request);
@@ -608,7 +608,7 @@ pub(crate) async fn inspect_pending_input(
                 #[allow(deprecated)]
                 cwd: turn_context.cwd.clone(),
                 transcript_path: sess.hook_transcript_path().await,
-                model: turn_context.model_info.slug.clone(),
+                model: turn_context.model_info().slug.clone(),
                 permission_mode: hook_permission_mode(turn_context),
                 prompt: UserMessageItem::new(content).message(),
             };
@@ -845,7 +845,7 @@ fn hook_run_analytics_payload(
 ) -> (codex_analytics::TrackEventsContext, HookRunFact) {
     (
         build_track_events_context(
-            turn_context.model_info.slug.clone(),
+            turn_context.model_info().slug.clone(),
             thread_id,
             completed
                 .turn_id
@@ -1071,7 +1071,7 @@ mod tests {
 
         assert_eq!(tracking.thread_id, "thread-123");
         assert_eq!(tracking.turn_id, "turn-from-hook");
-        assert_eq!(tracking.model_slug, turn_context.model_info.slug);
+        assert_eq!(tracking.model_slug, turn_context.model_info().slug);
         assert_eq!(hook.event_name, HookEventName::Stop);
         assert_eq!(hook.handler_type, HookHandlerType::Command);
         assert_eq!(hook.execution_mode, HookExecutionMode::Sync);
diff --git a/codex-rs/core/src/mcp_tool_call.rs b/codex-rs/core/src/mcp_tool_call.rs
index 2bbb831ad7..1b9057478c 100644
--- a/codex-rs/core/src/mcp_tool_call.rs
+++ b/codex-rs/core/src/mcp_tool_call.rs
@@ -287,7 +287,7 @@ pub(crate) async fn handle_mcp_tool_call(
                     &call_id,
                     invocation,
                     item_metadata.clone(),
-                    crate::guardian::guardian_timeout_message(&turn_context.model_info),
+                    crate::guardian::guardian_timeout_message(turn_context.model_info()),
                     /*already_started*/ true,
                 )
                 .await
@@ -449,7 +449,7 @@ async fn handle_approved_mcp_tool_call(
                         .map(|(connector_id, action_name)| HostedFileUploadContext {
                             connector_id: connector_id.clone(),
                             action_name: action_name.clone(),
-                            model: turn_context.model_info.slug.clone(),
+                            model: turn_context.model_info().slug.clone(),
                         });
                     let rewritten_arguments = rewrite_mcp_tool_arguments_for_openai_files(
                         sess,
@@ -491,7 +491,7 @@ async fn handle_approved_mcp_tool_call(
                 .await
                 .map_err(|error| format!("tool call error: {error:?}"))?;
             let result = sanitize_mcp_tool_result_for_model(
-                &turn_context.model_info.input_modalities,
+                &turn_context.model_info().input_modalities,
                 Ok(result),
             )?;
             Ok(maybe_request_codex_apps_auth_elicitation(
@@ -1023,7 +1023,7 @@ async fn maybe_track_codex_app_used(
     };
 
     let tracking = build_track_events_context(
-        turn_context.model_info.slug.clone(),
+        turn_context.model_info().slug.clone(),
         sess.thread_id.to_string(),
         turn_context.sub_id.clone(),
         turn_context.originator.clone(),
@@ -1193,7 +1193,7 @@ fn build_mcp_tool_call_request_meta(
     if let Some(turn_metadata) = turn_context
         .turn_metadata_state
         .current_meta_value_for_mcp_request(McpTurnMetadataContext {
-            model: turn_context.model_info.slug.as_str(),
+            model: turn_context.model_info().slug.as_str(),
             reasoning_effort: turn_context.effective_reasoning_effort(),
         })
     {
@@ -1317,7 +1317,7 @@ async fn maybe_request_mcp_tool_approval(
     let approvals_reviewer = connectors::mcp_approvals_reviewer_from_layers(
         &config.config_layer_stack,
         config.approvals_reviewer,
-        Some(turn_context.model_info.slug.as_str()),
+        Some(turn_context.model_info().slug.as_str()),
         &invocation.server,
         metadata.connector_id.as_deref(),
     );
diff --git a/codex-rs/core/src/mcp_tool_call_tests.rs b/codex-rs/core/src/mcp_tool_call_tests.rs
index 9748432eb1..e8fd9f9f46 100644
--- a/codex-rs/core/src/mcp_tool_call_tests.rs
+++ b/codex-rs/core/src/mcp_tool_call_tests.rs
@@ -93,7 +93,7 @@ fn approval_config(turn_context: &TurnContext) -> codex_mcp::McpConfig {
 
 fn mcp_turn_metadata_context(turn_context: &TurnContext) -> McpTurnMetadataContext<'_> {
     McpTurnMetadataContext {
-        model: turn_context.model_info.slug.as_str(),
+        model: turn_context.model_info().slug.as_str(),
         reasoning_effort: turn_context.effective_reasoning_effort(),
     }
 }
@@ -1038,15 +1038,15 @@ async fn mcp_tool_call_request_meta_includes_turn_metadata_for_custom_server() {
         turn_metadata
             .get("model")
             .and_then(serde_json::Value::as_str),
-        Some(turn_context.model_info.slug.as_str())
+        Some(turn_context.model_info().slug.as_str())
     );
     assert_eq!(
         turn_metadata["node_repl_auto_review_required"],
-        serde_json::Value::Bool(turn_context.model_info.node_repl_auto_review_required),
+        serde_json::Value::Bool(turn_context.model_info().node_repl_auto_review_required),
     );
     assert_eq!(
         turn_metadata["node_repl_disabled"],
-        serde_json::Value::Bool(turn_context.model_info.node_repl_disabled),
+        serde_json::Value::Bool(turn_context.model_info().node_repl_disabled),
     );
     assert_eq!(
         turn_metadata
@@ -2496,7 +2496,7 @@ async fn permission_request_hook_allows_mcp_tool_call() {
             "turn_id": "turn_id",
             "cwd": turn_cwd,
             "transcript_path": null,
-            "model": turn_context.model_info.slug,
+            "model": turn_context.model_info().slug,
             "permission_mode": "default",
             "tool_name": "mcp__memory__create_entities",
             "hook_event_name": "PermissionRequest",
@@ -2566,7 +2566,7 @@ async fn permission_request_hook_uses_hook_tool_name_without_metadata() {
             "turn_id": "turn_id",
             "cwd": turn_cwd,
             "transcript_path": null,
-            "model": turn_context.model_info.slug,
+            "model": turn_context.model_info().slug,
             "permission_mode": "default",
             "tool_name": "mcp__memory__create_entities",
             "hook_event_name": "PermissionRequest",
diff --git a/codex-rs/core/src/prompt_debug.rs b/codex-rs/core/src/prompt_debug.rs
index 7e91ee81ad..125315283a 100644
--- a/codex-rs/core/src/prompt_debug.rs
+++ b/codex-rs/core/src/prompt_debug.rs
@@ -101,7 +101,7 @@ pub(crate) async fn build_prompt_input_from_session(
     let prompt_input = sess
         .clone_history()
         .await
-        .for_prompt(&step_context.model_info.input_modalities);
+        .for_prompt(&step_context.settings.model_info.input_modalities);
     let base_instructions = sess.get_base_instructions().await;
     let prompt = build_prompt(prompt_input, step_context.as_ref(), base_instructions);
 
diff --git a/codex-rs/core/src/responses_retry.rs b/codex-rs/core/src/responses_retry.rs
index 178c13df49..fb0505411e 100644
--- a/codex-rs/core/src/responses_retry.rs
+++ b/codex-rs/core/src/responses_retry.rs
@@ -85,7 +85,7 @@ pub(crate) async fn handle_retryable_response_stream_error(
     if retry_state.retries >= max_retries
         && client_session.try_switch_fallback_transport(
             &turn_context.session_telemetry,
-            &turn_context.model_info,
+            turn_context.model_info(),
         )
     {
         sess.send_event(
diff --git a/codex-rs/core/src/session/context_window.rs b/codex-rs/core/src/session/context_window.rs
index 466175c17d..ae9e4676a5 100644
--- a/codex-rs/core/src/session/context_window.rs
+++ b/codex-rs/core/src/session/context_window.rs
@@ -31,7 +31,7 @@ pub(crate) async fn context_window_token_status(
         match turn_context.config.model_auto_compact_token_limit_scope {
             AutoCompactTokenLimitScope::Total => (
                 active_context_tokens,
-                turn_context.model_info.auto_compact_token_limit(),
+                turn_context.model_info().auto_compact_token_limit(),
                 None,
             ),
             AutoCompactTokenLimitScope::BodyAfterPrefix => {
@@ -41,7 +41,7 @@ pub(crate) async fn context_window_token_status(
                 let scope_limit = turn_context
                     .config
                     .model_auto_compact_token_limit
-                    .or_else(|| turn_context.model_info.auto_compact_token_limit());
+                    .or_else(|| turn_context.model_info().auto_compact_token_limit());
                 (
                     active_context_tokens.saturating_sub(baseline),
                     scope_limit,
diff --git a/codex-rs/core/src/session/handlers.rs b/codex-rs/core/src/session/handlers.rs
index 28fbc46b3c..de495d99c9 100644
--- a/codex-rs/core/src/session/handlers.rs
+++ b/codex-rs/core/src/session/handlers.rs
@@ -119,12 +119,8 @@ pub async fn run_user_shell_command(sess: &Arc<Session>, sub_id: String, command
     }
 
     let turn_context = sess.new_default_turn_with_sub_id(sub_id).await;
-    sess.spawn_task(
-        Arc::clone(&turn_context),
-        Vec::new(),
-        UserShellCommandTask::new(command),
-    )
-    .await;
+    sess.spawn_task(turn_context, Vec::new(), UserShellCommandTask::new(command))
+        .await;
 }
 
 pub async fn resolve_elicitation(
@@ -243,8 +239,7 @@ pub async fn reload_user_config(sess: &Arc<Session>) {
 pub async fn compact(sess: &Arc<Session>, sub_id: String) {
     let turn_context = sess.new_default_turn_with_sub_id(sub_id).await;
 
-    sess.spawn_task(Arc::clone(&turn_context), Vec::new(), CompactTask)
-        .await;
+    sess.spawn_task(turn_context, Vec::new(), CompactTask).await;
 }
 
 pub async fn thread_rollback(sess: &Arc<Session>, sub_id: String, num_turns: u32) {
diff --git a/codex-rs/core/src/session/mcp.rs b/codex-rs/core/src/session/mcp.rs
index dcb5c399ba..847f6e21da 100644
--- a/codex-rs/core/src/session/mcp.rs
+++ b/codex-rs/core/src/session/mcp.rs
@@ -766,7 +766,7 @@ async fn review_guardian_mcp_elicitation(
             || crate::connectors::mcp_approvals_reviewer_from_layers(
                 &mcp_config.config_layer_stack,
                 ApprovalsReviewer::AutoReview,
-                Some(turn_context.model_info.slug.as_str()),
+                Some(turn_context.model_info().slug.as_str()),
                 request.server_name.as_str(),
                 connector_id,
             ) != ApprovalsReviewer::AutoReview
@@ -806,7 +806,7 @@ async fn review_guardian_mcp_elicitation(
                 | ReviewDecision::Abort
         )
         .then(|| {
-            mcp_elicitation_response_from_guardian_decision(decision, &turn_context.model_info)
+            mcp_elicitation_response_from_guardian_decision(decision, turn_context.model_info())
         }));
     }
 
@@ -844,7 +844,7 @@ async fn review_guardian_mcp_elicitation(
     let approvals_reviewer = crate::connectors::mcp_approvals_reviewer_from_layers(
         &mcp_config.config_layer_stack,
         mcp_config.approvals_reviewer,
-        Some(turn_context.model_info.slug.as_str()),
+        Some(turn_context.model_info().slug.as_str()),
         request.server_name.as_str(),
         elicitation_connector_id(&request.elicitation),
     );
@@ -882,7 +882,7 @@ async fn review_guardian_mcp_elicitation(
     .await;
     Ok(Some(mcp_elicitation_response_from_guardian_decision(
         decision,
-        &turn_context.model_info,
+        turn_context.model_info(),
     )))
 }
 
diff --git a/codex-rs/core/src/session/mod.rs b/codex-rs/core/src/session/mod.rs
index 3d180b03a9..2373476fbc 100644
--- a/codex-rs/core/src/session/mod.rs
+++ b/codex-rs/core/src/session/mod.rs
@@ -1379,7 +1379,7 @@ impl Session {
                     .await;
 
                 // If resuming, warn when the last recorded model differs from the current one.
-                let curr: &str = turn_context.model_info.slug.as_str();
+                let curr: &str = turn_context.model_info().slug.as_str();
                 if let Some(prev) = previous_turn_settings
                     .as_ref()
                     .map(|settings| settings.model.as_str())
@@ -3069,7 +3069,7 @@ impl Session {
         let mut items = items.to_vec();
         let image_preparation_mode = if unified_image_budget_enabled(
             &turn_context.config.features,
-            &turn_context.model_info,
+            turn_context.model_info(),
         ) {
             ImagePreparationMode::UnifiedBudget
         } else {
@@ -3202,7 +3202,7 @@ impl Session {
                 .note_recorded_items(&response_items);
             state
                 .history
-                .record_annotated_items(&items, turn_context.model_info.truncation_policy.into());
+                .record_annotated_items(&items, turn_context.model_info().truncation_policy.into());
         }
         for image in image_preparations {
             self.services
@@ -3286,6 +3286,10 @@ impl Session {
         cancellation_token: &CancellationToken,
         required_servers: &[String],
     ) -> CodexResult<Arc<StepContext>> {
+        // Capture once before asynchronous planning; all request consumers
+        // retain this immutable settings version even if the turn is updated.
+        let settings = turn_context.current_settings.load_full();
+        let session_telemetry = settings.telemetry(&turn_context.session_telemetry);
         // Keep selections fixed for the turn while allowing their startup work to finish.
         let environments = turn_context.environments.refresh_readiness();
         self.services
@@ -3354,6 +3358,8 @@ impl Session {
         });
         extension_data.insert(selected_plugins.clone());
         turn_context.extension_data.insert(selected_plugins);
+        // Tool planning still uses the admitted turn. Migrating it to the
+        // captured model is a separate step from diagnostic activation.
         let tool_router = turn::built_tools(
             self.as_ref(),
             turn_context.as_ref(),
@@ -3365,13 +3371,8 @@ impl Session {
         .or_cancel(cancellation_token)
         .await??;
         Ok(Arc::new(StepContext {
-            model_info: Arc::clone(&turn_context.model_info),
-            reasoning_effort: turn_context.reasoning_effort.clone(),
-            reasoning_summary: turn_context.reasoning_summary,
-            service_tier: turn_context.config.service_tier.clone(),
-            approval_policy: turn_context.approval_policy(),
-            approvals_reviewer: turn_context.config.approvals_reviewer,
-            session_telemetry: turn_context.session_telemetry.clone(),
+            settings,
+            session_telemetry,
             turn: turn_context,
             environments,
             selected_capability_roots,
@@ -3399,7 +3400,7 @@ impl Session {
             state.current_time_reminder.note_recorded_items(items);
             state.record_items(
                 items.iter(),
-                turn_context.model_info.truncation_policy.into(),
+                turn_context.model_info().truncation_policy.into(),
             );
         }
         self.persist_rollout_items(&[
@@ -3414,10 +3415,11 @@ impl Session {
 
     async fn maybe_warn_on_server_model_mismatch(
         self: &Arc<Self>,
-        turn_context: &Arc<TurnContext>,
+        step_context: &StepContext,
         server_model: String,
     ) -> bool {
-        let requested_model = turn_context.model_info.slug.clone();
+        let turn_context = &step_context.turn;
+        let requested_model = step_context.settings.model_info.slug.clone();
         let server_model_normalized = server_model.to_ascii_lowercase();
         let requested_model_normalized = requested_model.to_ascii_lowercase();
         if server_model_normalized == requested_model_normalized {
diff --git a/codex-rs/core/src/session/multi_agents.rs b/codex-rs/core/src/session/multi_agents.rs
index bae1969159..22d56df390 100644
--- a/codex-rs/core/src/session/multi_agents.rs
+++ b/codex-rs/core/src/session/multi_agents.rs
@@ -73,7 +73,7 @@ pub(super) fn usage_hint_text(
     }
 
     let catalog = turn_context
-        .model_info
+        .model_info()
         .model_messages
         .as_ref()
         .and_then(|messages| messages.multi_agent.as_ref())
@@ -148,7 +148,7 @@ pub(crate) fn effective_multi_agent_mode(turn_context: &TurnContext) -> Option<M
     }
 
     let catalog_mode = turn_context
-        .model_info
+        .model_info()
         .model_messages
         .as_ref()
         .and_then(|messages| messages.multi_agent.as_ref())
diff --git a/codex-rs/core/src/session/review.rs b/codex-rs/core/src/session/review.rs
index ca2853e198..b634e7510e 100644
--- a/codex-rs/core/src/session/review.rs
+++ b/codex-rs/core/src/session/review.rs
@@ -1,4 +1,6 @@
+use super::step_settings::ResolvedStepSettings;
 use super::*;
+use arc_swap::ArcSwap;
 use std::sync::atomic::AtomicBool;
 
 /// Spawn a review thread using the given prompt.
@@ -12,7 +14,7 @@ pub(super) async fn spawn_review_thread(
     let model = config
         .review_model
         .clone()
-        .unwrap_or_else(|| parent_turn_context.model_info.slug.clone());
+        .unwrap_or_else(|| parent_turn_context.model_info().slug.clone());
     let available_models = sess
         .services
         .models_manager
@@ -43,15 +45,16 @@ pub(super) async fn spawn_review_thread(
     let provider = parent_turn_context.provider.clone();
     let auth_manager = parent_turn_context.auth_manager.clone();
     let model_info = review_model_info.clone();
+    let mut selected = parent_turn_context.initial_settings.selected().clone();
+    let mut reasoning_effort = selected.collaboration_mode.reasoning_effort();
 
     // Build per‑turn client with the requested model/family.
     let mut per_turn_config = (*parent_turn_context.config).clone();
     // Preserve configured overrides without carrying over the parent model's defaults.
     per_turn_config.token_budget = config.token_budget.clone();
-    per_turn_config.model = Some(model.clone());
     per_turn_config.features = review_features.clone();
-    if let Some(current_effort) = per_turn_config.model_reasoning_effort.as_ref()
-        && review_model_info.slug != parent_turn_context.model_info.slug
+    if let Some(current_effort) = reasoning_effort.as_ref()
+        && review_model_info.slug != parent_turn_context.model_info().slug
         && !review_model_info.used_fallback_model_metadata
         && !review_model_info
             .supported_reasoning_levels
@@ -59,7 +62,7 @@ pub(super) async fn spawn_review_thread(
             .any(|preset| &preset.effort == current_effort)
     {
         let supported_reasoning_levels = &review_model_info.supported_reasoning_levels;
-        per_turn_config.model_reasoning_effort = supported_reasoning_levels
+        reasoning_effort = supported_reasoning_levels
             .get(supported_reasoning_levels.len().saturating_sub(1) / 2)
             .map(|preset| preset.effort.clone())
             .or_else(|| review_model_info.default_reasoning_level.clone());
@@ -74,17 +77,8 @@ pub(super) async fn spawn_review_thread(
         );
     }
 
-    let session_telemetry = parent_turn_context
-        .session_telemetry
-        .clone()
-        .with_model(model.as_str(), review_model_info.slug.as_str());
     let auth_manager_for_context = auth_manager.clone();
     let provider_for_context = provider.clone();
-    let session_telemetry_for_context = session_telemetry.clone();
-    let reasoning_effort = per_turn_config.model_reasoning_effort.clone();
-    let reasoning_summary = per_turn_config
-        .model_reasoning_summary
-        .unwrap_or(model_info.default_reasoning_summary);
     let session_source = parent_turn_context.session_source.clone();
     let (forked_from_thread_id, thread_source, service_tier) = {
         let state = sess.state.lock().await;
@@ -99,12 +93,25 @@ pub(super) async fn spawn_review_thread(
                 .or_else(|| config.service_tier.clone()),
         )
     };
-    per_turn_config.service_tier = service_tier;
-
     let auto_review_enabled = crate::guardian::routes_approval_policy_to_guardian(
         per_turn_config.permissions.approval_policy.value(),
         per_turn_config.approvals_reviewer,
     );
+    // The original config may retain a requested tier unsupported by the parent
+    // model. Resolve it against the review model and the shared feature gate.
+    selected.collaboration_mode.settings.model = model.clone();
+    selected.collaboration_mode.settings.reasoning_effort = reasoning_effort.clone();
+    selected.service_tier = service_tier;
+    let step_settings = Arc::new(ResolvedStepSettings::new(
+        Arc::new(selected),
+        Arc::new(model_info.clone()),
+        review_features.enabled(Feature::FastMode),
+    ));
+    per_turn_config.model = Some(model);
+    per_turn_config.model_reasoning_effort = reasoning_effort;
+    per_turn_config.service_tier = step_settings.service_tier.clone();
+    let session_telemetry_for_context =
+        step_settings.telemetry(&parent_turn_context.session_telemetry);
     let per_turn_config = Arc::new(per_turn_config);
     let review_turn_id = sub_id.to_string();
     let turn_metadata_state = Arc::new(TurnMetadataState::new(
@@ -139,11 +146,10 @@ pub(super) async fn spawn_review_thread(
         code_mode_available: parent_turn_context.code_mode_available,
         config: per_turn_config,
         auth_manager: auth_manager_for_context,
-        model_info: Arc::new(model_info.clone()),
+        initial_settings: Arc::clone(&step_settings),
+        current_settings: ArcSwap::from(step_settings),
         session_telemetry: session_telemetry_for_context,
         provider: provider_for_context,
-        reasoning_effort,
-        reasoning_summary,
         session_source,
         history_mode: parent_turn_context.history_mode,
         parent_thread_id: parent_turn_context.parent_thread_id,
@@ -155,12 +161,7 @@ pub(super) async fn spawn_review_thread(
         timezone: parent_turn_context.timezone.clone(),
         app_server_client_name: parent_turn_context.app_server_client_name.clone(),
         developer_instructions: None,
-        mode: parent_turn_context.mode,
-        collaboration_mode_developer_instructions: parent_turn_context
-            .collaboration_mode_developer_instructions
-            .clone(),
         multi_agent_version: MultiAgentVersion::Disabled,
-        personality: parent_turn_context.personality,
         network: parent_turn_context.network.clone(),
         windows_sandbox_level: parent_turn_context.windows_sandbox_level,
         #[allow(deprecated)]
@@ -191,7 +192,8 @@ pub(super) async fn spawn_review_thread(
     // TODO(ccunningham): Review turns currently rely on `spawn_task` for TurnComplete but do not
     // emit a parent TurnStarted. Consider giving review a full parent turn lifecycle
     // (TurnStarted + TurnComplete) for consistency with other standalone tasks.
-    sess.spawn_task(tc.clone(), input, ReviewTask::new()).await;
+    sess.spawn_task(Arc::clone(&tc), input, ReviewTask::new())
+        .await;
 
     // Announce entering review mode so UIs can switch modes.
     let item = TurnItem::EnteredReviewMode(EnteredReviewModeItem {
diff --git a/codex-rs/core/src/session/rollout_reconstruction.rs b/codex-rs/core/src/session/rollout_reconstruction.rs
index 3896fa2e2e..66e0cf27ce 100644
--- a/codex-rs/core/src/session/rollout_reconstruction.rs
+++ b/codex-rs/core/src/session/rollout_reconstruction.rs
@@ -331,14 +331,14 @@ impl Session {
                 RolloutItem::ResponseItem(response_item) => {
                     history.record_annotated_items(
                         std::slice::from_ref(response_item),
-                        turn_context.model_info.truncation_policy.into(),
+                        turn_context.model_info().truncation_policy.into(),
                     );
                 }
                 RolloutItem::InterAgentCommunication(communication) => {
                     let response_item = communication.to_model_input_item();
                     history.record_items(
                         std::iter::once(&response_item),
-                        turn_context.model_info.truncation_policy.into(),
+                        turn_context.model_info().truncation_policy.into(),
                     );
                 }
                 RolloutItem::InterAgentCommunicationMetadata { .. } => {}
diff --git a/codex-rs/core/src/session/rollout_reconstruction_tests.rs b/codex-rs/core/src/session/rollout_reconstruction_tests.rs
index 034c72c3cb..5447999e15 100644
--- a/codex-rs/core/src/session/rollout_reconstruction_tests.rs
+++ b/codex-rs/core/src/session/rollout_reconstruction_tests.rs
@@ -241,12 +241,12 @@ async fn record_initial_history_resumed_bare_turn_context_does_not_hydrate_previ
         file_system_sandbox_policy: None,
         model: previous_model.to_string(),
         comp_hash: None,
-        personality: turn_context.personality,
+        personality: turn_context.personality(),
         collaboration_mode: Some(turn_context.collaboration_mode()),
         multi_agent_version: None,
         multi_agent_mode: None,
         realtime_active: Some(turn_context.realtime_active),
-        effort: turn_context.reasoning_effort.clone(),
+        effort: turn_context.reasoning_effort().cloned(),
         summary: codex_protocol::config_types::ReasoningSummary::Auto,
     };
     let rollout_items = vec![RolloutItem::TurnContext(previous_context_item)];
@@ -289,12 +289,12 @@ async fn record_initial_history_resumed_hydrates_previous_turn_settings_from_lif
         file_system_sandbox_policy: None,
         model: previous_model.to_string(),
         comp_hash: Some("comp-hash-a".to_string()),
-        personality: turn_context.personality,
+        personality: turn_context.personality(),
         collaboration_mode: Some(turn_context.collaboration_mode()),
         multi_agent_version: None,
         multi_agent_mode: None,
         realtime_active: Some(turn_context.realtime_active),
-        effort: turn_context.reasoning_effort.clone(),
+        effort: turn_context.reasoning_effort().cloned(),
         summary: codex_protocol::config_types::ReasoningSummary::Auto,
     };
     let turn_id = previous_context_item
@@ -464,7 +464,7 @@ async fn reconstruct_history_rollback_keeps_history_and_metadata_in_sync_for_com
     assert_eq!(
         reconstructed.previous_turn_settings,
         Some(PreviousTurnSettings {
-            model: turn_context.model_info.slug.clone(),
+            model: turn_context.model_info().slug.clone(),
             comp_hash: None,
             realtime_active: Some(turn_context.realtime_active),
         })
@@ -565,7 +565,7 @@ async fn reconstruct_history_rollback_keeps_history_and_metadata_in_sync_for_inc
     assert_eq!(
         reconstructed.previous_turn_settings,
         Some(PreviousTurnSettings {
-            model: turn_context.model_info.slug.clone(),
+            model: turn_context.model_info().slug.clone(),
             comp_hash: None,
             realtime_active: Some(turn_context.realtime_active),
         })
@@ -697,7 +697,7 @@ async fn reconstruct_history_rollback_skips_non_user_turns_for_history_and_metad
     assert_eq!(
         reconstructed.previous_turn_settings,
         Some(PreviousTurnSettings {
-            model: turn_context.model_info.slug.clone(),
+            model: turn_context.model_info().slug.clone(),
             comp_hash: None,
             realtime_active: Some(turn_context.realtime_active),
         })
@@ -802,7 +802,7 @@ async fn reconstruct_history_rollback_counts_inter_agent_assistant_turns() {
     assert_eq!(
         reconstructed.previous_turn_settings,
         Some(PreviousTurnSettings {
-            model: turn_context.model_info.slug.clone(),
+            model: turn_context.model_info().slug.clone(),
             comp_hash: None,
             realtime_active: Some(turn_context.realtime_active),
         })
@@ -1036,7 +1036,7 @@ async fn record_initial_history_resumed_rollback_drops_incomplete_user_turn_comp
     assert_eq!(
         session.previous_turn_settings().await,
         Some(PreviousTurnSettings {
-            model: turn_context.model_info.slug.clone(),
+            model: turn_context.model_info().slug.clone(),
             comp_hash: None,
             realtime_active: Some(turn_context.realtime_active),
         })
@@ -1360,12 +1360,12 @@ async fn record_initial_history_resumed_turn_context_after_compaction_reestablis
         file_system_sandbox_policy: None,
         model: previous_model.to_string(),
         comp_hash: None,
-        personality: turn_context.personality,
+        personality: turn_context.personality(),
         collaboration_mode: Some(turn_context.collaboration_mode()),
         multi_agent_version: None,
         multi_agent_mode: None,
         realtime_active: Some(turn_context.realtime_active),
-        effort: turn_context.reasoning_effort.clone(),
+        effort: turn_context.reasoning_effort().cloned(),
         summary: codex_protocol::config_types::ReasoningSummary::Auto,
     };
     let previous_turn_id = previous_context_item
@@ -1451,12 +1451,12 @@ async fn record_initial_history_resumed_turn_context_after_compaction_reestablis
             file_system_sandbox_policy: None,
             model: previous_model.to_string(),
             comp_hash: None,
-            personality: turn_context.personality,
+            personality: turn_context.personality(),
             collaboration_mode: Some(turn_context.collaboration_mode()),
             multi_agent_version: None,
             multi_agent_mode: None,
             realtime_active: Some(turn_context.realtime_active),
-            effort: turn_context.reasoning_effort.clone(),
+            effort: turn_context.reasoning_effort().cloned(),
             summary: codex_protocol::config_types::ReasoningSummary::Auto,
         }))
         .expect("serialize expected reference context item")
@@ -1484,12 +1484,12 @@ async fn record_initial_history_resumed_aborted_turn_without_id_clears_active_tu
         file_system_sandbox_policy: None,
         model: previous_model.to_string(),
         comp_hash: None,
-        personality: turn_context.personality,
+        personality: turn_context.personality(),
         collaboration_mode: Some(turn_context.collaboration_mode()),
         multi_agent_version: None,
         multi_agent_mode: None,
         realtime_active: Some(turn_context.realtime_active),
-        effort: turn_context.reasoning_effort.clone(),
+        effort: turn_context.reasoning_effort().cloned(),
         summary: codex_protocol::config_types::ReasoningSummary::Auto,
     };
     let previous_turn_id = previous_context_item
@@ -1616,12 +1616,12 @@ async fn record_initial_history_resumed_unmatched_abort_preserves_active_turn_fo
         file_system_sandbox_policy: None,
         model: current_model.to_string(),
         comp_hash: None,
-        personality: turn_context.personality,
+        personality: turn_context.personality(),
         collaboration_mode: Some(turn_context.collaboration_mode()),
         multi_agent_version: None,
         multi_agent_mode: None,
         realtime_active: Some(turn_context.realtime_active),
-        effort: turn_context.reasoning_effort.clone(),
+        effort: turn_context.reasoning_effort().cloned(),
         summary: codex_protocol::config_types::ReasoningSummary::Auto,
     };
 
@@ -1744,12 +1744,12 @@ async fn record_initial_history_resumed_trailing_incomplete_turn_compaction_clea
         file_system_sandbox_policy: None,
         model: previous_model.to_string(),
         comp_hash: None,
-        personality: turn_context.personality,
+        personality: turn_context.personality(),
         collaboration_mode: Some(turn_context.collaboration_mode()),
         multi_agent_version: None,
         multi_agent_mode: None,
         realtime_active: Some(turn_context.realtime_active),
-        effort: turn_context.reasoning_effort.clone(),
+        effort: turn_context.reasoning_effort().cloned(),
         summary: codex_protocol::config_types::ReasoningSummary::Auto,
     };
     let previous_turn_id = previous_context_item
@@ -1882,7 +1882,7 @@ async fn record_initial_history_resumed_trailing_incomplete_turn_preserves_turn_
     assert_eq!(
         session.previous_turn_settings().await,
         Some(PreviousTurnSettings {
-            model: turn_context.model_info.slug.clone(),
+            model: turn_context.model_info().slug.clone(),
             comp_hash: None,
             realtime_active: Some(turn_context.realtime_active),
         })
@@ -1916,12 +1916,12 @@ async fn record_initial_history_resumed_replaced_incomplete_compacted_turn_clear
         file_system_sandbox_policy: None,
         model: previous_model.to_string(),
         comp_hash: None,
-        personality: turn_context.personality,
+        personality: turn_context.personality(),
         collaboration_mode: Some(turn_context.collaboration_mode()),
         multi_agent_version: None,
         multi_agent_mode: None,
         realtime_active: Some(turn_context.realtime_active),
-        effort: turn_context.reasoning_effort.clone(),
+        effort: turn_context.reasoning_effort().cloned(),
         summary: codex_protocol::config_types::ReasoningSummary::Auto,
     };
     let previous_turn_id = previous_context_item
diff --git a/codex-rs/core/src/session/step_context.rs b/codex-rs/core/src/session/step_context.rs
index 8ab12c1860..41c65c5c31 100644
--- a/codex-rs/core/src/session/step_context.rs
+++ b/codex-rs/core/src/session/step_context.rs
@@ -2,35 +2,19 @@ use std::sync::Arc;
 
 use crate::agents_md::LoadedAgentsMd;
 use crate::environment_selection::TurnEnvironmentSnapshot;
+use crate::session::step_settings::ResolvedStepSettings;
 use crate::session::turn_context::TurnContext;
 use crate::tools::router::ToolRouter;
 use codex_exec_server::ExecutorCapabilityDiscoverySnapshot;
 use codex_exec_server::ResolvedSelectedCapabilityRoot;
 use codex_mcp::McpBinding;
 use codex_otel::SessionTelemetry;
-use codex_protocol::config_types::ApprovalsReviewer;
-use codex_protocol::config_types::ReasoningSummary;
-use codex_protocol::openai_models::ModelInfo;
-use codex_protocol::openai_models::ReasoningEffort;
-use codex_protocol::protocol::AskForApproval;
 
 /// Request-scoped state that may change between model sampling requests.
 pub(crate) struct StepContext {
     pub(crate) turn: Arc<TurnContext>,
-    /// Concrete model and capabilities used by this sampling request.
-    pub(crate) model_info: Arc<ModelInfo>,
-    /// Reasoning effort selected for this sampling request.
-    pub(crate) reasoning_effort: Option<ReasoningEffort>,
-    /// Reasoning summary resolved for this sampling request.
-    pub(crate) reasoning_summary: ReasoningSummary,
-    /// Effective service tier supported by this sampling request's model.
-    pub(crate) service_tier: Option<String>,
-    /// Effective approval policy used by this sampling request's tool actions.
-    /// Model-specific Guardian requirements can change this during a model switch.
-    pub(crate) approval_policy: AskForApproval,
-    /// Effective reviewer selected for this sampling request's approvals.
-    /// Model-specific Guardian requirements can change this during a model switch.
-    pub(crate) approvals_reviewer: ApprovalsReviewer,
+    /// One immutable settings version captured before request preparation.
+    pub(crate) settings: Arc<ResolvedStepSettings>,
     /// Telemetry context tagged with this sampling request's model.
     pub(crate) session_telemetry: SessionTelemetry,
     pub(crate) environments: TurnEnvironmentSnapshot,
diff --git a/codex-rs/core/src/session/step_settings.rs b/codex-rs/core/src/session/step_settings.rs
index 484ee756bb..7d52a2ad0e 100644
--- a/codex-rs/core/src/session/step_settings.rs
+++ b/codex-rs/core/src/session/step_settings.rs
@@ -1,32 +1,117 @@
-//! Configured inputs used to derive effective step settings.
+//! Configured inputs retained independently of future thread settings.
 
 use crate::config::Constrained;
 use crate::config::ConstraintError;
 use crate::config::ConstraintResult;
 use codex_config::ConfigRequirements;
 use codex_models_manager::ModelsManagerConfig;
+use codex_models_manager::manager::ModelsManager;
+use codex_otel::SessionTelemetry;
 use codex_protocol::config_types::ApprovalsReviewer;
 use codex_protocol::config_types::CollaborationMode;
 use codex_protocol::config_types::Personality;
 use codex_protocol::config_types::ReasoningSummary;
 use codex_protocol::config_types::SERVICE_TIER_DEFAULT_REQUEST_VALUE;
 use codex_protocol::config_types::ServiceTier;
+use codex_protocol::openai_models::ModelInfo;
 use codex_protocol::openai_models::ReasoningEffort;
 use codex_protocol::protocol::AskForApproval;
+use std::sync::Arc;
 
 /// Model and execution settings selected for an individual model step within
 /// a turn. A turn may contain several steps, each using its own captured settings.
 #[derive(Clone, Debug, PartialEq)]
 pub(crate) struct StepSettings {
     pub(crate) collaboration_mode: CollaborationMode,
+    /// `None` follows the pinned model's default.
     pub(crate) reasoning_summary: Option<ReasoningSummary>,
+    /// Normalized requested tier. Startup retains initial-model filtering;
+    /// resolution filters the effective tier against the pinned model.
     pub(crate) service_tier: Option<String>,
     pub(crate) personality: Option<Personality>,
     pub(crate) approval_policy: Constrained<AskForApproval>,
     pub(crate) approvals_reviewer: ApprovalsReviewer,
 }
 
+/// Immutable configured choices, pinned model metadata, and effective request values.
+///
+/// One snapshot may produce several fresh `StepContext`s. Replacing the
+/// snapshot does not change steps or actions that have already captured it.
+#[derive(Clone, Debug)]
+pub(crate) struct ResolvedStepSettings {
+    /// Inputs for later sparse patches. Unset defaults and unsupported requested
+    /// tiers must not be reconstructed from the effective values below.
+    selected: Arc<StepSettings>,
+    pub(crate) model_info: Arc<ModelInfo>,
+    /// Effective request summary: the configured value or the pinned model's default.
+    pub(crate) reasoning_summary: ReasoningSummary,
+    /// Tier sent on requests, filtered by feature and model support.
+    pub(crate) service_tier: Option<String>,
+}
+
+impl ResolvedStepSettings {
+    /// Derives request values from selected settings and pinned metadata.
+    pub(super) fn new(
+        selected: Arc<StepSettings>,
+        model_info: Arc<ModelInfo>,
+        fast_mode_enabled: bool,
+    ) -> Self {
+        let reasoning_summary = selected
+            .reasoning_summary
+            .unwrap_or(model_info.default_reasoning_summary);
+        let service_tier = super::get_service_tier(
+            selected.service_tier.clone(),
+            fast_mode_enabled,
+            &model_info,
+        );
+        Self {
+            selected,
+            model_info,
+            reasoning_summary,
+            service_tier,
+        }
+    }
+
+    pub(crate) fn reasoning_effort(&self) -> Option<&ReasoningEffort> {
+        self.selected
+            .collaboration_mode
+            .settings
+            .reasoning_effort
+            .as_ref()
+    }
+
+    pub(crate) fn approval_policy(&self) -> AskForApproval {
+        self.selected.approval_policy.value()
+    }
+
+    pub(crate) fn approvals_reviewer(&self) -> ApprovalsReviewer {
+        self.selected.approvals_reviewer
+    }
+
+    /// Retained inputs for constructing a snapshot against different model metadata.
+    pub(super) fn selected(&self) -> &StepSettings {
+        &self.selected
+    }
+
+    pub(super) fn selected_collaboration_mode(&self) -> &CollaborationMode {
+        &self.selected.collaboration_mode
+    }
+
+    pub(super) fn personality(&self) -> Option<Personality> {
+        self.selected.personality
+    }
+
+    pub(super) fn telemetry(&self, base: &SessionTelemetry) -> SessionTelemetry {
+        base.clone().with_model(
+            self.selected.collaboration_mode.model(),
+            &self.model_info.slug,
+        )
+    }
+}
+
 /// Explicit startup overrides applied to catalog-derived model metadata.
+/// Construct from `Config::to_models_manager_config()` so model-derived base
+/// instructions are not mistaken for explicit overrides.
 #[derive(Clone, Debug, Default, PartialEq, Eq)]
 pub(crate) struct ModelInfoOverrides {
     pub(crate) context_window: Option<i64>,
@@ -83,6 +168,8 @@ pub(crate) struct StepSettingsUpdate {
 }
 
 /// Constraints used when applying and validating a candidate settings version.
+/// Future settings use the proposed environment; active settings use the
+/// environment already admitted for that execution.
 pub(crate) struct StepSettingsConstraints<'a> {
     pub(crate) requirements: &'a ConfigRequirements,
     pub(crate) guardian_approval_enabled: bool,
@@ -91,6 +178,19 @@ pub(crate) struct StepSettingsConstraints<'a> {
 }
 
 impl StepSettings {
+    /// Resolves the selected model using the session's explicit startup overrides.
+    pub(super) async fn resolve_model_info(
+        &self,
+        models_manager: &dyn ModelsManager,
+        overrides: &ModelInfoOverrides,
+        personality_enabled: bool,
+    ) -> ModelInfo {
+        let config = overrides.models_manager_config(self.personality, personality_enabled);
+        models_manager
+            .get_model_info(self.collaboration_mode.model(), &config)
+            .await
+    }
+
     /// Applies edits and validates the result against the supplied constraints.
     /// Callers must supply the constraints of the proposed target environment.
     pub(crate) fn apply(
@@ -182,4 +282,4 @@ impl StepSettings {
 
 #[cfg(test)]
 #[path = "step_settings_tests.rs"]
-mod tests;
+pub(super) mod tests;
diff --git a/codex-rs/core/src/session/step_settings_tests.rs b/codex-rs/core/src/session/step_settings_tests.rs
index 778a6edc52..eb75b3c730 100644
--- a/codex-rs/core/src/session/step_settings_tests.rs
+++ b/codex-rs/core/src/session/step_settings_tests.rs
@@ -1,5 +1,6 @@
 use super::*;
 use crate::config::PermissionProfileState;
+use crate::config::test_config;
 use crate::session::session::SessionConfiguration;
 use crate::session::session::SessionSettingsUpdate;
 use crate::session::tests::make_session_configuration_for_tests;
@@ -7,9 +8,17 @@ use codex_config::ConfigLayerStack;
 use codex_config::RequirementSource;
 use codex_config::Sourced;
 use codex_features::Feature;
+use codex_models_manager::manager::StaticModelsManager;
+use codex_models_manager::model_info::model_info_from_slug;
 use codex_protocol::config_types::ModeKind;
 use codex_protocol::config_types::Settings;
+use codex_protocol::models::BaseInstructionsProvenance;
 use codex_protocol::models::PermissionProfile;
+use codex_protocol::openai_models::AutoReviewMessages;
+use codex_protocol::openai_models::GuardianV2ModelConfig;
+use codex_protocol::openai_models::ModelInstructionsVariables;
+use codex_protocol::openai_models::ModelsResponse;
+use codex_protocol::openai_models::TruncationPolicyConfig;
 use codex_protocol::permissions::FileSystemAccessMode;
 use codex_protocol::permissions::FileSystemPath;
 use codex_protocol::permissions::FileSystemSandboxEntry;
@@ -22,6 +31,14 @@ use core_test_support::test_codex::local;
 use pretty_assertions::assert_eq;
 use std::collections::BTreeSet;
 use std::sync::Arc;
+use test_case::test_case;
+
+pub(crate) fn update_selected_settings_for_test(
+    settings: &mut ResolvedStepSettings,
+    update: impl FnOnce(&mut StepSettings),
+) {
+    update(Arc::make_mut(&mut settings.selected));
+}
 
 fn set_requirements(configuration: &mut SessionConfiguration, requirements: ConfigRequirements) {
     let config = Arc::make_mut(&mut configuration.original_config_do_not_use);
@@ -383,3 +400,109 @@ fn collaboration_replacement_wins_and_effort_clear_remains_sparse() {
         }
     );
 }
+
+#[test_case(BaseInstructionsProvenance::Custom; "explicit instructions")]
+#[test_case(BaseInstructionsProvenance::Model { model: "model-a".to_string() }; "model-derived instructions")]
+#[tokio::test]
+async fn model_resolution_preserves_startup_overrides_and_instruction_provenance(
+    provenance: BaseInstructionsProvenance,
+) {
+    let configured_instructions = "explicit {{ personality }}";
+    let auto_review = AutoReviewMessages {
+        policy: Some("catalog review policy".to_string()),
+        policy_template: Some("catalog review template".to_string()),
+        rejection_instructions: None,
+        timeout_instructions: None,
+    };
+    let guardian_v2 = GuardianV2ModelConfig {
+        classifier_instructions: Some("catalog classifier".to_string()),
+        review_threshold_basis_points: Some(7_500),
+        ..Default::default()
+    };
+    let mut model = model_info_from_slug("model-b");
+    model.context_window = Some(90_000);
+    model.max_context_window = Some(100_000);
+    model.auto_compact_token_limit = Some(80_000);
+    model.truncation_policy = TruncationPolicyConfig::tokens(/*limit*/ 1_000);
+    let messages = model
+        .model_messages
+        .as_mut()
+        .expect("test model should have instruction metadata");
+    messages.instructions_template =
+        Some("Catalog B.\n# Personality\n{{ personality }}\n# Rules\nKeep the rules.".to_string());
+    messages.instructions_variables = Some(ModelInstructionsVariables {
+        personality_default: Some("default".to_string()),
+        personality_friendly: Some("friendly".to_string()),
+        personality_pragmatic: Some("pragmatic".to_string()),
+    });
+    messages.auto_review = Some(auto_review);
+    messages.guardian_v2 = Some(guardian_v2);
+    let catalog = ModelsResponse {
+        models: vec![model],
+    };
+    let models_manager = StaticModelsManager::new(/*auth_manager*/ None, catalog.clone());
+
+    let mut config = test_config().await;
+    config.model = Some("model-a".to_string());
+    config.model_catalog = Some(catalog);
+    config.model_context_window = Some(160_000);
+    config.model_auto_compact_token_limit = Some(70_000);
+    config.tool_output_token_limit = Some(777);
+    config.base_instructions = Some(configured_instructions.to_string());
+    let explicit_instructions = matches!(&provenance, BaseInstructionsProvenance::Custom);
+    config.base_instructions_provenance = Some(provenance);
+
+    // Capture the same filtered explicit overrides that session startup owns.
+    let overrides = ModelInfoOverrides::from(config.to_models_manager_config());
+
+    for (personality, personality_enabled, catalog_instructions) in [
+        (
+            Personality::Friendly,
+            true,
+            "Catalog B.\n# Personality\nfriendly\n# Rules\nKeep the rules.",
+        ),
+        (
+            Personality::None,
+            true,
+            "Catalog B.\n# Rules\nKeep the rules.",
+        ),
+        (
+            Personality::Friendly,
+            false,
+            "Catalog B.\n# Personality\ndefault\n# Rules\nKeep the rules.",
+        ),
+    ] {
+        config.personality = Some(personality);
+        config
+            .features
+            .set_enabled(Feature::Personality, personality_enabled)
+            .expect("test config should allow personality changes");
+        let mut settings = configured_settings();
+        settings.collaboration_mode = settings.collaboration_mode.with_updates(
+            Some("model-b".to_string()),
+            /*effort*/ None,
+            /*developer_instructions*/ None,
+        );
+        settings.personality = config.personality;
+
+        let legacy = models_manager
+            .get_model_info("model-b", &config.to_models_manager_config())
+            .await;
+        let resolved = settings
+            .resolve_model_info(
+                &models_manager,
+                &overrides,
+                config.features.enabled(Feature::Personality),
+            )
+            .await;
+        assert_eq!(resolved, legacy);
+        assert_eq!(
+            resolved.get_model_instructions(settings.personality),
+            if explicit_instructions {
+                configured_instructions
+            } else {
+                catalog_instructions
+            },
+        );
+    }
+}
diff --git a/codex-rs/core/src/session/tests.rs b/codex-rs/core/src/session/tests.rs
index 8f29343d14..e9af213209 100644
--- a/codex-rs/core/src/session/tests.rs
+++ b/codex-rs/core/src/session/tests.rs
@@ -1,6 +1,8 @@
 use super::mcp_refresh::McpRefresh;
+use super::step_settings::ResolvedStepSettings;
 use super::step_settings::StepSettings;
 use super::step_settings::StepSettingsUpdate;
+pub(crate) use super::step_settings::tests::update_selected_settings_for_test;
 use super::turn_context::TurnEnvironment;
 use super::*;
 use crate::agents_md_manager::AgentsMdManager;
@@ -212,16 +214,31 @@ pub(crate) fn mcp_config_for_test(config: &crate::config::Config) -> Arc<codex_m
     ))
 }
 
+/// Updates both initial/current views before sharing a test turn context.
+pub(crate) fn update_turn_settings_for_test(
+    turn: &mut TurnContext,
+    update: impl FnOnce(&mut super::step_settings::ResolvedStepSettings),
+) {
+    let mut settings = turn.initial_settings.as_ref().clone();
+    update(&mut settings);
+    let settings = Arc::new(settings);
+    turn.initial_settings = Arc::clone(&settings);
+    turn.current_settings.store(settings);
+}
+
 impl StepContext {
     pub(crate) fn for_test(turn: Arc<TurnContext>) -> Arc<Self> {
         let environments = turn.environments.clone();
+        // Unit fixtures still customize the legacy Config directly.
+        // Production capture instead takes the turn's current snapshot.
+        let mut settings = turn.initial_settings.as_ref().clone();
+        update_selected_settings_for_test(&mut settings, |selected| {
+            selected.approval_policy = turn.config.permissions.approval_policy.clone();
+            selected.approvals_reviewer = turn.config.approvals_reviewer;
+        });
+        settings.service_tier = turn.config.service_tier.clone();
         Arc::new(Self {
-            model_info: Arc::clone(&turn.model_info),
-            reasoning_effort: turn.reasoning_effort.clone(),
-            reasoning_summary: turn.reasoning_summary,
-            service_tier: turn.config.service_tier.clone(),
-            approval_policy: turn.approval_policy(),
-            approvals_reviewer: turn.config.approvals_reviewer,
+            settings: Arc::new(settings),
             session_telemetry: turn.session_telemetry.clone(),
             turn: Arc::clone(&turn),
             environments,
@@ -496,7 +513,7 @@ async fn world_state_extension_metrics_follow_turn_model_switch() {
         .session_telemetry
         .clone()
         .with_metrics(metrics.clone());
-    let next_model = if turn_context.model_info.slug == "gpt-5.4" {
+    let next_model = if turn_context.model_info().slug == "gpt-5.4" {
         "gpt-5.2"
     } else {
         "gpt-5.4"
@@ -2890,8 +2907,10 @@ async fn recompute_token_usage_updates_model_context_window() {
         }));
     }
 
-    Arc::make_mut(&mut turn_context.model_info).context_window = Some(128_000);
-    Arc::make_mut(&mut turn_context.model_info).effective_context_window_percent = 100;
+    update_turn_settings_for_test(&mut turn_context, |settings| {
+        Arc::make_mut(&mut settings.model_info).context_window = Some(128_000);
+        Arc::make_mut(&mut settings.model_info).effective_context_window_percent = 100;
+    });
 
     session.recompute_token_usage(&turn_context).await;
 
@@ -3655,12 +3674,12 @@ async fn record_initial_history_forked_hydrates_previous_turn_settings() {
         file_system_sandbox_policy: None,
         model: previous_model.to_string(),
         comp_hash: None,
-        personality: turn_context.personality,
+        personality: turn_context.personality(),
         collaboration_mode: Some(turn_context.collaboration_mode()),
         multi_agent_version: None,
         multi_agent_mode: None,
         realtime_active: Some(turn_context.realtime_active),
-        effort: turn_context.reasoning_effort.clone(),
+        effort: turn_context.reasoning_effort().cloned(),
         summary: codex_protocol::config_types::ReasoningSummary::Auto,
     };
     let turn_id = previous_context_item
@@ -3962,7 +3981,7 @@ async fn thread_rollback_recomputes_previous_turn_settings_and_reference_context
     assert_eq!(
         sess.previous_turn_settings().await,
         Some(PreviousTurnSettings {
-            model: tc.model_info.slug.clone(),
+            model: tc.model_info().slug.clone(),
             comp_hash: None,
             realtime_active: Some(tc.realtime_active),
         })
@@ -4585,7 +4604,7 @@ async fn includes_timed_out_message() {
     };
     let (_, turn_context) = make_session_and_context().await;
 
-    let out = format_exec_output_str(&exec, turn_context.model_info.truncation_policy.into());
+    let out = format_exec_output_str(&exec, turn_context.model_info().truncation_policy.into());
 
     assert_eq!(
         out,
@@ -4596,7 +4615,38 @@ async fn includes_timed_out_message() {
 #[tokio::test]
 async fn turn_context_with_model_updates_model_fields() {
     let (session, mut turn_context) = make_session_and_context().await;
-    turn_context.reasoning_effort = Some(ReasoningEffortConfig::Minimal);
+    let config = Arc::make_mut(&mut turn_context.config);
+    config.features.enable(Feature::FastMode).unwrap();
+    config.model_reasoning_effort = Some(ReasoningEffortConfig::Minimal);
+    config.model_reasoning_summary = Some(ReasoningSummaryConfig::Detailed);
+    update_turn_settings_for_test(&mut turn_context, |settings| {
+        let mut selected = settings.selected().clone();
+        selected.collaboration_mode.settings.reasoning_effort =
+            Some(ReasoningEffortConfig::Minimal);
+        selected.reasoning_summary = Some(ReasoningSummaryConfig::Detailed);
+        selected.service_tier = Some(ServiceTier::Fast.request_value().to_string());
+        *settings = ResolvedStepSettings::new(
+            Arc::new(selected),
+            Arc::clone(&settings.model_info),
+            /*fast_mode_enabled*/ true,
+        );
+    });
+    Arc::make_mut(&mut turn_context.config).service_tier =
+        turn_context.initial_settings.service_tier.clone();
+    let captured = turn_context.current_settings.load_full();
+    let mut current_selection = captured.selected().clone();
+    current_selection.reasoning_summary = Some(ReasoningSummaryConfig::None);
+    current_selection.service_tier = None;
+    current_selection
+        .collaboration_mode
+        .settings
+        .reasoning_effort = Some(ReasoningEffortConfig::High);
+    let current = Arc::new(ResolvedStepSettings::new(
+        Arc::new(current_selection),
+        Arc::clone(turn_context.model_info()),
+        /*fast_mode_enabled*/ true,
+    ));
+    turn_context.current_settings.store(Arc::clone(&current));
     let updated = turn_context
         .with_model("gpt-5.4".to_string(), &session.services.models_manager)
         .await;
@@ -4609,12 +4659,48 @@ async fn turn_context_with_model_updates_model_fields() {
         )
         .await;
 
+    // Historical model selection starts from the frozen turn settings, not a
+    // later publication, and retains its selected summary/tier.
+    assert_eq!(
+        (
+            updated.reasoning_summary(),
+            updated.initial_settings.service_tier.as_deref()
+        ),
+        (
+            ReasoningSummaryConfig::Detailed,
+            Some(ServiceTier::Fast.request_value())
+        ),
+    );
+    assert_eq!(
+        (
+            updated.config.model_reasoning_summary,
+            updated.config.service_tier.as_deref()
+        ),
+        (
+            Some(ReasoningSummaryConfig::Detailed),
+            Some(ServiceTier::Fast.request_value())
+        ),
+    );
+    assert!(Arc::ptr_eq(&captured, &turn_context.initial_settings));
+    assert!(Arc::ptr_eq(
+        &current,
+        &turn_context.current_settings.load_full()
+    ));
+    assert!(!Arc::ptr_eq(&captured, &updated.initial_settings));
+    assert!(Arc::ptr_eq(
+        &updated.initial_settings,
+        &updated.current_settings.load_full()
+    ));
+    assert!(!Arc::ptr_eq(
+        &updated.current_settings.load_full(),
+        &turn_context.current_settings.load_full()
+    ));
     assert_eq!(updated.config.model.as_deref(), Some("gpt-5.4"));
     assert_eq!(updated.collaboration_mode().model(), "gpt-5.4");
-    assert_eq!(updated.model_info.as_ref(), &expected_model_info);
+    assert_eq!(updated.model_info().as_ref(), &expected_model_info);
     assert_eq!(
-        updated.reasoning_effort,
-        Some(ReasoningEffortConfig::Medium)
+        updated.reasoning_effort(),
+        Some(&ReasoningEffortConfig::Medium)
     );
     assert_eq!(
         updated.collaboration_mode().reasoning_effort(),
@@ -6251,7 +6337,11 @@ pub(crate) async fn make_session_and_context() -> (Session, TurnContext) {
         session.services.shell_zsh_path.as_ref(),
         session.services.main_execve_wrapper_exe.as_ref(),
         per_turn_config,
-        model_info,
+        Arc::new(super::step_settings::ResolvedStepSettings::new(
+            Arc::clone(&session_configuration.step_settings),
+            Arc::new(model_info),
+            config.features.enabled(Feature::FastMode),
+        )),
         &models_manager,
         /*network*/ None,
         resolved_turn_environments,
@@ -8476,7 +8566,11 @@ where
         session.services.shell_zsh_path.as_ref(),
         session.services.main_execve_wrapper_exe.as_ref(),
         per_turn_config,
-        model_info,
+        Arc::new(super::step_settings::ResolvedStepSettings::new(
+            Arc::clone(&session_configuration.step_settings),
+            Arc::new(model_info),
+            config.features.enabled(Feature::FastMode),
+        )),
         &models_manager,
         /*network*/ None,
         resolved_turn_environments,
@@ -9137,7 +9231,7 @@ async fn record_context_updates_emits_environment_item_for_network_changes() {
     let previous_context = Arc::new(previous_context);
     let mut current_context = previous_context
         .with_model(
-            previous_context.model_info.slug.clone(),
+            previous_context.model_info().slug.clone(),
             &session.services.models_manager,
         )
         .await;
@@ -9193,7 +9287,7 @@ async fn record_context_updates_emits_environment_item_for_cwd_changes() {
     let previous_context = Arc::new(previous_context);
     let mut current_context = previous_context
         .with_model(
-            previous_context.model_info.slug.clone(),
+            previous_context.model_info().slug.clone(),
             &session.services.models_manager,
         )
         .await;
@@ -9250,7 +9344,7 @@ async fn record_context_updates_use_environment_permission_profile_and_workspace
     let previous_context = Arc::new(previous_context);
     let mut current_context = previous_context
         .with_model(
-            previous_context.model_info.slug.clone(),
+            previous_context.model_info().slug.clone(),
             &session.services.models_manager,
         )
         .await;
@@ -9304,7 +9398,7 @@ async fn record_context_updates_emits_environment_item_for_time_changes() {
     let previous_context = Arc::new(previous_context);
     let mut current_context = previous_context
         .with_model(
-            previous_context.model_info.slug.clone(),
+            previous_context.model_info().slug.clone(),
             &session.services.models_manager,
         )
         .await;
@@ -9328,7 +9422,7 @@ async fn record_context_updates_omits_environment_item_when_disabled() {
     let previous_context = Arc::new(previous_context);
     let mut current_context = previous_context
         .with_model(
-            previous_context.model_info.slug.clone(),
+            previous_context.model_info().slug.clone(),
             &session.services.models_manager,
         )
         .await;
@@ -9393,7 +9487,7 @@ async fn record_context_updates_emits_realtime_start_when_session_becomes_live()
     let previous_context = Arc::new(previous_context);
     let mut current_context = previous_context
         .with_model(
-            previous_context.model_info.slug.clone(),
+            previous_context.model_info().slug.clone(),
             &session.services.models_manager,
         )
         .await;
@@ -9417,7 +9511,7 @@ async fn record_context_updates_emits_realtime_end_when_session_stops_being_live
     previous_context.realtime_active = true;
     let mut current_context = previous_context
         .with_model(
-            previous_context.model_info.slug.clone(),
+            previous_context.model_info().slug.clone(),
             &session.services.models_manager,
         )
         .await;
@@ -9561,8 +9655,10 @@ async fn build_initial_context_includes_turn_context_fragments_from_extensions()
     let mut builder = codex_extension_api::ExtensionRegistryBuilder::new();
     builder.prompt_contributor(Arc::new(TurnContextExtensionTestContributor));
     session.services.extensions = Arc::new(builder.build());
-    Arc::make_mut(&mut turn_context.model_info).context_window = Some(100);
-    Arc::make_mut(&mut turn_context.model_info).effective_context_window_percent = 50;
+    update_turn_settings_for_test(&mut turn_context, |settings| {
+        Arc::make_mut(&mut settings.model_info).context_window = Some(100);
+        Arc::make_mut(&mut settings.model_info).effective_context_window_percent = 50;
+    });
     turn_context
         .extension_data
         .insert(TurnContextExtensionTestState {
@@ -9588,8 +9684,10 @@ async fn record_context_updates_includes_turn_context_fragments_on_steady_state_
     let mut builder = codex_extension_api::ExtensionRegistryBuilder::new();
     builder.prompt_contributor(Arc::new(TurnContextExtensionTestContributor));
     session.services.extensions = Arc::new(builder.build());
-    Arc::make_mut(&mut turn_context.model_info).context_window = Some(200);
-    Arc::make_mut(&mut turn_context.model_info).effective_context_window_percent = 25;
+    update_turn_settings_for_test(&mut turn_context, |settings| {
+        Arc::make_mut(&mut settings.model_info).context_window = Some(200);
+        Arc::make_mut(&mut settings.model_info).effective_context_window_percent = 25;
+    });
     turn_context
         .extension_data
         .insert(TurnContextExtensionTestState {
@@ -9770,7 +9868,7 @@ async fn build_initial_context_restates_realtime_start_when_reference_context_is
     let (session, mut turn_context) = make_session_and_context().await;
     turn_context.realtime_active = true;
     let previous_turn_settings = PreviousTurnSettings {
-        model: turn_context.model_info.slug.clone(),
+        model: turn_context.model_info().slug.clone(),
         comp_hash: None,
         realtime_active: Some(true),
     };
@@ -10121,7 +10219,7 @@ async fn build_initial_context_prepends_model_switch_message() {
 async fn record_context_updates_and_set_reference_context_item_persists_full_reinjection_to_rollout()
  {
     let (mut session, previous_context) = make_session_and_context().await;
-    let next_model = if previous_context.model_info.slug == "gpt-5.4" {
+    let next_model = if previous_context.model_info().slug == "gpt-5.4" {
         "gpt-5.2"
     } else {
         "gpt-5.4"
@@ -10150,7 +10248,7 @@ async fn record_context_updates_and_set_reference_context_item_persists_full_rei
 
     session
         .set_previous_turn_settings(Some(PreviousTurnSettings {
-            model: previous_context.model_info.slug.clone(),
+            model: previous_context.model_info().slug.clone(),
             comp_hash: None,
             realtime_active: Some(previous_context.realtime_active),
         }))
@@ -11402,10 +11500,10 @@ async fn sample_rollout(
             && content.iter().any(|c| {
                 matches!(c, ContentItem::InputText { text } if text.contains("<personality_spec>"))
             }))
-    }) && let Some(p) = reconstruction_turn.personality
+    }) && let Some(p) = reconstruction_turn.personality()
         && session.features.enabled(Feature::Personality)
         && let Some(personality_message) = reconstruction_turn
-            .model_info
+            .model_info()
             .model_messages
             .as_ref()
             .and_then(|m| m.get_personality_message(Some(p)).filter(|s| !s.is_empty()))
@@ -11425,20 +11523,20 @@ async fn sample_rollout(
     }
     live_history.record_items(
         initial_context.iter(),
-        reconstruction_turn.model_info.truncation_policy.into(),
+        reconstruction_turn.model_info().truncation_policy.into(),
     );
 
     let user1 = user_message("first user");
     live_history.record_items(
         std::iter::once(&user1),
-        reconstruction_turn.model_info.truncation_policy.into(),
+        reconstruction_turn.model_info().truncation_policy.into(),
     );
     rollout_items.push(RolloutItem::ResponseItem(user1.clone().into()));
 
     let assistant1 = assistant_message("assistant reply one");
     live_history.record_items(
         std::iter::once(&assistant1),
-        reconstruction_turn.model_info.truncation_policy.into(),
+        reconstruction_turn.model_info().truncation_policy.into(),
     );
     rollout_items.push(RolloutItem::ResponseItem(assistant1.clone().into()));
 
@@ -11461,14 +11559,14 @@ async fn sample_rollout(
     let user2 = user_message("second user");
     live_history.record_items(
         std::iter::once(&user2),
-        reconstruction_turn.model_info.truncation_policy.into(),
+        reconstruction_turn.model_info().truncation_policy.into(),
     );
     rollout_items.push(RolloutItem::ResponseItem(user2.clone().into()));
 
     let assistant2 = assistant_message("assistant reply two");
     live_history.record_items(
         std::iter::once(&assistant2),
-        reconstruction_turn.model_info.truncation_policy.into(),
+        reconstruction_turn.model_info().truncation_policy.into(),
     );
     rollout_items.push(RolloutItem::ResponseItem(assistant2.clone().into()));
 
@@ -11491,14 +11589,14 @@ async fn sample_rollout(
     let user3 = user_message("third user");
     live_history.record_items(
         std::iter::once(&user3),
-        reconstruction_turn.model_info.truncation_policy.into(),
+        reconstruction_turn.model_info().truncation_policy.into(),
     );
     rollout_items.push(RolloutItem::ResponseItem(user3.into()));
 
     let assistant3 = assistant_message("assistant reply three");
     live_history.record_items(
         std::iter::once(&assistant3),
-        reconstruction_turn.model_info.truncation_policy.into(),
+        reconstruction_turn.model_info().truncation_policy.into(),
     );
     rollout_items.push(RolloutItem::ResponseItem(assistant3.into()));
 
diff --git a/codex-rs/core/src/session/tests/guardian_tests.rs b/codex-rs/core/src/session/tests/guardian_tests.rs
index c982a0a128..1371f55915 100644
--- a/codex-rs/core/src/session/tests/guardian_tests.rs
+++ b/codex-rs/core/src/session/tests/guardian_tests.rs
@@ -5,6 +5,7 @@ use crate::guardian::GUARDIAN_REVIEWER_NAME;
 use crate::plugins::plugins_manager_for_config;
 use crate::sandboxing::SandboxPermissions;
 use crate::session::step_context::StepContext;
+use crate::session::tests::update_turn_settings_for_test;
 use crate::test_support::models_manager_with_provider;
 use crate::tools::context::ToolCallSource;
 use crate::tools::context::ToolOutput;
@@ -97,7 +98,9 @@ async fn request_permissions_routes_to_guardian_when_reviewer_is_enabled() {
     .await;
 
     let (mut session, mut turn_context_raw) = make_session_and_context().await;
-    Arc::make_mut(&mut turn_context_raw.model_info).node_repl_auto_review_required = true;
+    update_turn_settings_for_test(&mut turn_context_raw, |settings| {
+        Arc::make_mut(&mut settings.model_info).node_repl_auto_review_required = true;
+    });
     *session.active_turn.lock().await = Some(ActiveTurn::default());
     Arc::make_mut(&mut turn_context_raw.config)
         .permissions
diff --git a/codex-rs/core/src/session/turn.rs b/codex-rs/core/src/session/turn.rs
index 850166360d..05b67cbe86 100644
--- a/codex-rs/core/src/session/turn.rs
+++ b/codex-rs/core/src/session/turn.rs
@@ -272,8 +272,8 @@ pub(crate) async fn run_turn(
     sess.merge_connector_selection(explicitly_enabled_connectors.clone())
         .await;
     sess.set_previous_turn_settings(Some(PreviousTurnSettings {
-        model: turn_context.model_info.slug.clone(),
-        comp_hash: turn_context.model_info.comp_hash.clone(),
+        model: turn_context.model_info().slug.clone(),
+        comp_hash: turn_context.model_info().comp_hash.clone(),
         realtime_active: Some(turn_context.realtime_active),
     }))
     .await;
@@ -372,7 +372,7 @@ pub(crate) async fn run_turn(
             let sampling_request_input: Vec<ResponseItem> = async {
                 sess.clone_history()
                     .await
-                    .for_prompt(&step_context.model_info.input_modalities)
+                    .for_prompt(&step_context.settings.model_info.input_modalities)
             }
             .instrument(trace_span!("run_turn.prepare_sampling_request_input"))
             .await;
@@ -782,7 +782,7 @@ async fn build_skills_and_plugins(
     }
 
     let tracking = build_track_events_context(
-        turn_context.model_info.slug.clone(),
+        turn_context.model_info().slug.clone(),
         sess.thread_id.to_string(),
         turn_context.sub_id.clone(),
         turn_context.originator.clone(),
@@ -999,13 +999,13 @@ async fn track_turn_resolved_config_analytics(
             submission_type: None,
             ephemeral: thread_config.ephemeral,
             session_source: thread_config.session_source,
-            model: turn_context.model_info.slug.clone(),
+            model: turn_context.model_info().slug.clone(),
             model_provider: turn_context.config.model_provider_id.clone(),
             permission_profile: turn_context.permission_profile(),
             #[allow(deprecated)]
             permission_profile_cwd: turn_context.cwd.to_path_buf(),
-            reasoning_effort: turn_context.reasoning_effort.clone(),
-            reasoning_summary: Some(turn_context.reasoning_summary),
+            reasoning_effort: turn_context.reasoning_effort().cloned(),
+            reasoning_summary: Some(turn_context.reasoning_summary()),
             service_tier: turn_context
                 .config
                 .service_tier
@@ -1014,8 +1014,8 @@ async fn track_turn_resolved_config_analytics(
             approval_policy: turn_context.approval_policy(),
             approvals_reviewer: turn_context.config.approvals_reviewer,
             sandbox_network_access: turn_context.network_sandbox_policy().is_enabled(),
-            collaboration_mode: turn_context.mode,
-            personality: turn_context.personality,
+            collaboration_mode: turn_context.mode(),
+            personality: turn_context.personality(),
             workspace_kind: turn_context.turn_metadata_state.workspace_kind(),
             is_first_turn,
         });
@@ -1077,7 +1077,7 @@ async fn capture_current_model_fallback_step_context(
         .is_some_and(codex_login::AuthManager::current_auth_uses_codex_backend);
     if !uses_codex_backend
         || !turn_context.provider.info().is_openai()
-        || previous_model == turn_context.model_info.slug
+        || previous_model == turn_context.model_info().slug
     {
         return Ok(None);
     }
@@ -1101,7 +1101,7 @@ async fn maybe_run_previous_model_inline_compact(
     };
     let should_compact_for_comp_hash_change = comp_hash_changed(
         previous_turn_settings.comp_hash.as_deref(),
-        turn_context.model_info.comp_hash.as_deref(),
+        turn_context.model_info().comp_hash.as_deref(),
     );
     let previous_model = previous_turn_settings.model;
     let previous_model_turn_context = Arc::new(
@@ -1147,7 +1147,7 @@ async fn maybe_run_previous_model_inline_compact(
     {
         AutoCompactTokenLimitScope::Total => {
             let new_auto_compact_limit = turn_context
-                .model_info
+                .model_info()
                 .auto_compact_token_limit()
                 .unwrap_or(i64::MAX);
             active_context_tokens > new_auto_compact_limit
@@ -1156,7 +1156,7 @@ async fn maybe_run_previous_model_inline_compact(
         AutoCompactTokenLimitScope::BodyAfterPrefix => active_context_tokens >= new_context_window,
     };
     let should_run = previous_model_limit_reached
-        && previous_model_turn_context.model_info.slug != turn_context.model_info.slug
+        && previous_model_turn_context.model_info().slug != turn_context.model_info().slug
         && old_context_window > new_context_window;
     if should_run {
         let step_context = sess
@@ -1346,7 +1346,7 @@ pub(crate) fn build_prompt(
     skip_all,
     fields(
         turn_id = %step_context.turn.sub_id,
-        model = %step_context.model_info.slug,
+        model = %step_context.settings.model_info.slug,
         cwd = %step_context.turn.cwd.display()
     )
 )]
@@ -1384,7 +1384,7 @@ async fn run_sampling_request(
         } else {
             sess.clone_history()
                 .await
-                .for_prompt(&step_context.model_info.input_modalities)
+                .for_prompt(&step_context.settings.model_info.input_modalities)
         };
         let mut prompt_input = prompt_input;
         if let Some(executed_tool_calls) = sess.services.executed_tool_calls.as_ref()
@@ -1500,7 +1500,7 @@ pub(crate) async fn prepare_tool_recommendations(
     skip_all,
     fields(
         turn_id = %turn_context.sub_id,
-        model = %turn_context.model_info.slug,
+        model = %turn_context.model_info().slug,
         apps_enabled = turn_context.apps_enabled()
     )
 )]
@@ -2186,7 +2186,7 @@ fn assign_missing_streamed_response_item_id(
     skip_all,
     fields(
         turn_id = %step_context.turn.sub_id,
-        model = %step_context.model_info.slug
+        model = %step_context.settings.model_info.slug
     )
 )]
 async fn try_run_sampling_request(
@@ -2202,16 +2202,16 @@ async fn try_run_sampling_request(
 ) -> CodexResult<SamplingRequestResult> {
     let turn_context = Arc::clone(&step_context.turn);
     feedback_tags!(
-        model = step_context.model_info.slug.clone(),
+        model = step_context.settings.model_info.slug.clone(),
         approval_policy = turn_context.approval_policy(),
         sandbox_policy = &turn_context.sandbox_policy(),
-        effort = step_context.reasoning_effort,
+        effort = step_context.settings.reasoning_effort(),
         auth_mode = sess.services.auth_manager.auth_mode(),
         features = sess.features.enabled_features(),
     );
     let inference_trace = sess.services.rollout_thread_trace.inference_trace_context(
         turn_context.sub_id.as_str(),
-        step_context.model_info.slug.as_str(),
+        step_context.settings.model_info.slug.as_str(),
         turn_context.provider.info().name.as_str(),
     );
     let sampling_timing_guard = turn_context.turn_timing_state.begin_sampling();
@@ -2223,11 +2223,11 @@ async fn try_run_sampling_request(
     let mut stream = client_session
         .stream(
             prompt,
-            &step_context.model_info,
+            &step_context.settings.model_info,
             &step_context.session_telemetry,
-            step_context.reasoning_effort.clone(),
-            step_context.reasoning_summary,
-            step_context.service_tier.clone(),
+            step_context.settings.reasoning_effort().cloned(),
+            step_context.settings.reasoning_summary,
+            step_context.settings.service_tier.clone(),
             responses_metadata,
             &inference_trace,
         )
@@ -2248,12 +2248,16 @@ async fn try_run_sampling_request(
     const MAX_ANALYTICS_TOOL_CALL_IDS_PER_RESPONSE: usize = 256;
     let mut analytics_tool_call_ids = Vec::new();
     let reasoning_effort = step_context
-        .reasoning_effort
-        .clone()
-        .or_else(|| step_context.model_info.default_reasoning_level.clone())
-        .map(|effort| effort.to_string())
+        .settings
+        .reasoning_effort()
+        .or(step_context
+            .settings
+            .model_info
+            .default_reasoning_level
+            .as_ref())
+        .map(std::string::ToString::to_string)
         .unwrap_or_else(|| "default".to_string());
-    let plan_mode = turn_context.mode == ModeKind::Plan;
+    let plan_mode = turn_context.mode() == ModeKind::Plan;
     let mut assistant_message_stream_parsers = AssistantMessageStreamParsers::new(plan_mode);
     let mut plan_mode_state = plan_mode.then(|| PlanModeStreamState::new(&turn_context.sub_id));
     let defer_streamed_turn_items_for_contributors =
@@ -2499,7 +2503,7 @@ async fn try_run_sampling_request(
                     .server_model_warning_emitted
                     .load(Ordering::Relaxed)
                     && sess
-                        .maybe_warn_on_server_model_mismatch(&turn_context, server_model)
+                        .maybe_warn_on_server_model_mismatch(&step_context, server_model)
                         .await
                 {
                     turn_context
@@ -2524,7 +2528,7 @@ async fn try_run_sampling_request(
                 sess.send_event(
                     &turn_context,
                     EventMsg::SafetyBuffering(SafetyBufferingEvent {
-                        model: turn_context.model_info.slug.clone(),
+                        model: step_context.settings.model_info.slug.clone(),
                         use_cases: buffering.use_cases,
                         reasons: buffering.reasons,
                         show_buffering_ui: buffering.show_buffering_ui,
diff --git a/codex-rs/core/src/session/turn_context.rs b/codex-rs/core/src/session/turn_context.rs
index 5041644280..7782e070d0 100644
--- a/codex-rs/core/src/session/turn_context.rs
+++ b/codex-rs/core/src/session/turn_context.rs
@@ -1,9 +1,11 @@
+use super::step_settings::ResolvedStepSettings;
 use super::*;
 use crate::environment_selection::EnvironmentConfigOrigin;
 use crate::environment_selection::TurnEnvironmentSnapshot;
 use crate::exec_policy::AllowPrefixRules;
 use crate::shell_snapshot::ShellSnapshotFile;
 use crate::tools::sandboxing::executor_windows_sandbox_level;
+use arc_swap::ArcSwap;
 use codex_core_plugins::PluginCommandAttribution;
 use codex_core_plugins::ResolvedPluginMetricsOperation;
 use codex_core_plugins::TrustedPluginRoots;
@@ -174,18 +176,17 @@ pub struct TurnContext {
     pub(crate) realtime_active: bool,
     pub(crate) code_mode_available: bool,
     /// Turn-scoped configuration. Read step-specific settings such as service tier and
-    /// approvals reviewer from the corresponding `StepContext` fields instead.
+    /// approvals reviewer from the corresponding `StepContext` instead.
     pub config: Arc<Config>,
     pub(crate) auth_manager: Option<Arc<AuthManager>>,
-    /// Legacy turn model; step-scoped execution should use `StepContext::model_info`.
-    pub(crate) model_info: Arc<ModelInfo>,
+    /// Frozen settings used to construct this context. Legacy turn consumers
+    /// keep this view even when later steps use different settings.
+    pub(crate) initial_settings: Arc<ResolvedStepSettings>,
+    /// Snapshot for the next step; request consumers use their captured StepContext.
+    pub(super) current_settings: ArcSwap<ResolvedStepSettings>,
     /// Turn-wide telemetry; model-attributed step work should use `StepContext::session_telemetry`.
     pub(crate) session_telemetry: SessionTelemetry,
     pub(crate) provider: SharedModelProvider,
-    /// Legacy turn effort; step-scoped execution should use `StepContext::reasoning_effort`.
-    pub(crate) reasoning_effort: Option<ReasoningEffortConfig>,
-    /// Legacy turn summary; step-scoped execution should use `StepContext::reasoning_summary`.
-    pub(crate) reasoning_summary: ReasoningSummaryConfig,
     pub(crate) session_source: SessionSource,
     pub(crate) history_mode: ThreadHistoryMode,
     pub(crate) parent_thread_id: Option<ThreadId>,
@@ -200,10 +201,7 @@ pub struct TurnContext {
     pub(crate) timezone: Option<String>,
     pub(crate) app_server_client_name: Option<String>,
     pub(crate) developer_instructions: Option<String>,
-    pub(crate) mode: ModeKind,
-    pub(crate) collaboration_mode_developer_instructions: Option<String>,
     pub(crate) multi_agent_version: MultiAgentVersion,
-    pub(crate) personality: Option<Personality>,
     pub(crate) network: Option<NetworkProxy>,
     // TODO(anp): Reconcile this parallel turn snapshot with TurnEnvironment::sandbox_context
     // so owner-provided environment settings govern the remaining sandbox decisions.
@@ -226,6 +224,46 @@ enum TurnMultiAgentRuntime {
 }
 
 impl TurnContext {
+    /// Legacy: returns the frozen initial-turn model metadata.
+    /// Step-scoped consumers should use their captured `StepContext::settings`.
+    pub(crate) fn model_info(&self) -> &Arc<ModelInfo> {
+        &self.initial_settings.model_info
+    }
+
+    /// Legacy: returns the frozen initial-turn reasoning-effort selection.
+    /// Step-scoped consumers should use their captured `StepContext::settings`.
+    pub(crate) fn reasoning_effort(&self) -> Option<&ReasoningEffortConfig> {
+        self.initial_settings.reasoning_effort()
+    }
+
+    /// Legacy: returns the frozen initial-turn effective reasoning summary.
+    /// Step-scoped consumers should use their captured `StepContext::settings`.
+    pub(crate) fn reasoning_summary(&self) -> ReasoningSummaryConfig {
+        self.initial_settings.reasoning_summary
+    }
+
+    /// Legacy: returns the frozen initial-turn collaboration mode kind.
+    /// Step-scoped consumers should use their captured `StepContext::settings`.
+    pub(crate) fn mode(&self) -> ModeKind {
+        self.initial_settings.selected_collaboration_mode().mode
+    }
+
+    /// Legacy: returns the frozen initial-turn personality.
+    /// Step-scoped consumers should use their captured `StepContext::settings`.
+    pub(crate) fn personality(&self) -> Option<Personality> {
+        self.initial_settings.personality()
+    }
+
+    /// Legacy: returns the frozen initial-turn collaboration-mode developer instructions.
+    /// Step-scoped consumers should use their captured `StepContext::settings`.
+    pub(crate) fn collaboration_mode_developer_instructions(&self) -> &Option<String> {
+        &self
+            .initial_settings
+            .selected_collaboration_mode()
+            .settings
+            .developer_instructions
+    }
+
     pub(crate) fn skills_snapshot(&self) -> Arc<HostSkillsSnapshot> {
         let Some(snapshot) = self.extension_data.get::<HostSkillsSnapshot>() else {
             unreachable!("every turn has a host skills snapshot");
@@ -233,13 +271,15 @@ impl TurnContext {
         snapshot
     }
 
+    /// Legacy: returns the frozen initial-turn collaboration mode with the resolved model slug.
+    /// Step-scoped consumers should use their captured `StepContext::settings`.
     pub(crate) fn collaboration_mode(&self) -> CollaborationMode {
         CollaborationMode {
-            mode: self.mode,
+            mode: self.mode(),
             settings: Settings {
-                model: self.model_info.slug.clone(),
-                reasoning_effort: self.reasoning_effort.clone(),
-                developer_instructions: self.collaboration_mode_developer_instructions.clone(),
+                model: self.model_info().slug.clone(),
+                reasoning_effort: self.reasoning_effort().cloned(),
+                developer_instructions: self.collaboration_mode_developer_instructions().clone(),
             },
         }
     }
@@ -266,12 +306,14 @@ impl TurnContext {
             .await
     }
 
-    /// Approval policy admitted with the turn; step-scoped actions should use
-    /// `StepContext::approval_policy` instead.
+    /// Legacy: returns the frozen initial-turn approval policy.
+    /// Step-scoped consumers should use their captured `StepContext::settings`.
     pub(crate) fn approval_policy(&self) -> AskForApproval {
         self.config.permissions.approval_policy.value()
     }
 
+    /// Legacy: returns the frozen initial-turn prefix-rule policy.
+    /// Step-scoped consumers should use their captured `StepContext::settings`.
     pub(crate) fn allow_prefix_rules(&self) -> AllowPrefixRules {
         let ignore_rules = self
             .config
@@ -280,8 +322,9 @@ impl TurnContext {
             .auto_review
             .as_ref()
             .and_then(|auto_review| auto_review.ignore_rules.as_ref())
-            .is_some_and(|models| models.contains(&self.model_info.slug));
-        if self.model_info.model_specialty.as_deref() == Some(MODEL_SPECIALTY_CYBER) || ignore_rules
+            .is_some_and(|models| models.contains(&self.model_info().slug));
+        if self.model_info().model_specialty.as_deref() == Some(MODEL_SPECIALTY_CYBER)
+            || ignore_rules
         {
             AllowPrefixRules::IgnoreForCyberModel
         } else {
@@ -354,21 +397,27 @@ impl TurnContext {
         workspace_roots
     }
 
+    /// Legacy: returns the frozen initial-turn reasoning effort, including the initial model default.
+    /// Step-scoped consumers should use their captured `StepContext::settings`.
     pub(crate) fn effective_reasoning_effort(&self) -> Option<ReasoningEffortConfig> {
-        self.reasoning_effort
-            .clone()
-            .or_else(|| self.model_info.default_reasoning_level.clone())
+        self.reasoning_effort()
+            .or(self.model_info().default_reasoning_level.as_ref())
+            .cloned()
     }
 
+    /// Legacy: returns the frozen initial-turn reasoning-effort label for tracing.
+    /// Step-scoped consumers should use their captured `StepContext::settings`.
     pub(crate) fn effective_reasoning_effort_for_tracing(&self) -> String {
         self.effective_reasoning_effort()
             .map(|effort| effort.to_string())
             .unwrap_or_else(|| "default".to_string())
     }
 
+    /// Legacy: returns the frozen initial-turn model context window.
+    /// Step-scoped consumers should use their captured `StepContext::settings`.
     pub(crate) fn model_context_window(&self) -> Option<i64> {
-        let effective_context_window_percent = self.model_info.effective_context_window_percent;
-        self.model_info
+        let effective_context_window_percent = self.model_info().effective_context_window_percent;
+        self.model_info()
             .resolved_context_window()
             .map(|context_window| {
                 context_window.saturating_mul(effective_context_window_percent) / 100
@@ -401,10 +450,9 @@ impl TurnContext {
             .iter()
             .map(|preset| preset.effort.clone())
             .collect::<Vec<_>>();
-        let reasoning_effort = if let Some(current_reasoning_effort) = self.reasoning_effort.clone()
-        {
-            if supported_reasoning_levels.contains(&current_reasoning_effort) {
-                Some(current_reasoning_effort)
+        let reasoning_effort = if let Some(current_reasoning_effort) = self.reasoning_effort() {
+            if supported_reasoning_levels.contains(current_reasoning_effort) {
+                Some(current_reasoning_effort.clone())
             } else {
                 supported_reasoning_levels
                     .get(supported_reasoning_levels.len().saturating_sub(1) / 2)
@@ -426,6 +474,19 @@ impl TurnContext {
             )
             .await;
         let model_info = Arc::new(model_info);
+        let mut selected = self.initial_settings.selected().clone();
+        selected.collaboration_mode = selected.collaboration_mode.with_updates(
+            Some(model),
+            Some(reasoning_effort),
+            /*developer_instructions*/ None,
+        );
+        let step_settings = Arc::new(ResolvedStepSettings::new(
+            Arc::new(selected),
+            model_info,
+            config.features.enabled(Feature::FastMode),
+        ));
+        config.service_tier = step_settings.service_tier.clone();
+        let session_telemetry = step_settings.telemetry(&self.session_telemetry);
 
         Self {
             sub_id: self.sub_id.clone(),
@@ -434,14 +495,10 @@ impl TurnContext {
             code_mode_available: self.code_mode_available,
             config: Arc::new(config),
             auth_manager: self.auth_manager.clone(),
-            model_info: Arc::clone(&model_info),
-            session_telemetry: self
-                .session_telemetry
-                .clone()
-                .with_model(model.as_str(), model_info.slug.as_str()),
+            initial_settings: Arc::clone(&step_settings),
+            current_settings: ArcSwap::from(step_settings),
+            session_telemetry,
             provider: self.provider.clone(),
-            reasoning_effort,
-            reasoning_summary: self.reasoning_summary,
             session_source: self.session_source.clone(),
             history_mode: self.history_mode,
             parent_thread_id: self.parent_thread_id,
@@ -453,12 +510,7 @@ impl TurnContext {
             timezone: self.timezone.clone(),
             app_server_client_name: self.app_server_client_name.clone(),
             developer_instructions: self.developer_instructions.clone(),
-            mode: self.mode,
-            collaboration_mode_developer_instructions: self
-                .collaboration_mode_developer_instructions
-                .clone(),
             multi_agent_version: self.multi_agent_version,
-            personality: self.personality,
             network: self.network.clone(),
             windows_sandbox_level: self.windows_sandbox_level,
             available_models,
@@ -517,14 +569,14 @@ impl TurnContext {
             ),
             network: self.turn_context_network_item(),
             file_system_sandbox_policy: self.non_legacy_file_system_sandbox_policy(),
-            model: self.model_info.slug.clone(),
-            comp_hash: self.model_info.comp_hash.clone(),
-            personality: self.personality,
+            model: self.model_info().slug.clone(),
+            comp_hash: self.model_info().comp_hash.clone(),
+            personality: self.personality(),
             collaboration_mode: Some(self.collaboration_mode()),
             multi_agent_version: Some(self.multi_agent_version),
             multi_agent_mode: None,
             realtime_active: Some(self.realtime_active),
-            effort: self.reasoning_effort.clone(),
+            effort: self.reasoning_effort().cloned(),
             summary: ReasoningSummaryConfig::Auto,
         }
     }
@@ -642,7 +694,7 @@ impl Session {
         shell_zsh_path: Option<&PathBuf>,
         main_execve_wrapper_exe: Option<&PathBuf>,
         per_turn_config: Config,
-        model_info: ModelInfo,
+        step_settings: Arc<ResolvedStepSettings>,
         models_manager: &SharedModelsManager,
         network: Option<NetworkProxy>,
         environments: TurnEnvironmentSnapshot,
@@ -650,21 +702,9 @@ impl Session {
         sub_id: String,
         skills_snapshot: HostSkillsSnapshot,
     ) -> TurnContext {
-        let collaboration_mode = &session_configuration.step_settings.collaboration_mode;
-        let reasoning_effort = collaboration_mode.reasoning_effort();
-        let reasoning_summary = session_configuration
-            .step_settings
-            .reasoning_summary
-            .unwrap_or(model_info.default_reasoning_summary);
-        let session_telemetry = session_telemetry.clone().with_model(
-            session_configuration
-                .step_settings
-                .collaboration_mode
-                .model(),
-            model_info.slug.as_str(),
-        );
+        let model_info = &step_settings.model_info;
+        let session_telemetry_for_context = step_settings.telemetry(session_telemetry);
         let session_source = session_configuration.session_source.clone();
-        let session_telemetry_for_context = session_telemetry;
         let available_models = models_manager.try_list_models().unwrap_or_default();
         let unified_exec_shell_mode = UnifiedExecShellMode::for_session(
             per_turn_config.features.get(),
@@ -674,12 +714,8 @@ impl Session {
         );
 
         let mut per_turn_config = per_turn_config;
-        super::token_budget::apply_model_defaults(&mut per_turn_config, &model_info);
-        per_turn_config.service_tier = get_service_tier(
-            per_turn_config.service_tier,
-            per_turn_config.features.enabled(Feature::FastMode),
-            &model_info,
-        );
+        super::token_budget::apply_model_defaults(&mut per_turn_config, model_info);
+        per_turn_config.service_tier = step_settings.service_tier.clone();
         let permission_profile = environments.permission_profile_or_else(|| {
             per_turn_config.permissions.effective_permission_profile()
         });
@@ -701,7 +737,7 @@ impl Session {
             session_configuration.windows_sandbox_level,
             network.is_some(),
             auto_review_enabled,
-            &model_info,
+            model_info,
         ));
         turn_metadata_state
             .set_responses_api_metadata(per_turn_config.responses_api_metadata.clone());
@@ -715,11 +751,10 @@ impl Session {
             code_mode_available: true,
             config: per_turn_config,
             auth_manager,
-            model_info: Arc::new(model_info),
+            initial_settings: Arc::clone(&step_settings),
+            current_settings: ArcSwap::from(step_settings),
             session_telemetry: session_telemetry_for_context,
             provider,
-            reasoning_effort,
-            reasoning_summary,
             session_source,
             history_mode: session_configuration.history_mode,
             parent_thread_id: session_configuration.parent_thread_id,
@@ -731,13 +766,7 @@ impl Session {
             timezone: Some(timezone),
             app_server_client_name: session_configuration.app_server_client_name.clone(),
             developer_instructions: session_configuration.developer_instructions.clone(),
-            mode: collaboration_mode.mode,
-            collaboration_mode_developer_instructions: collaboration_mode
-                .settings
-                .developer_instructions
-                .clone(),
             multi_agent_version,
-            personality: session_configuration.step_settings.personality,
             network,
             windows_sandbox_level: session_configuration.windows_sandbox_level,
             available_models,
@@ -758,13 +787,13 @@ impl Session {
         sub_id: String,
         updates: SessionSettingsUpdate,
     ) -> CodexResult<(Arc<TurnContext>, ThreadSettingsSnapshot)> {
-        let Some(turn) = self
+        let Some((turn_context, snapshot)) = self
             .new_turn_with_sub_id_if(sub_id, updates, |_, _| true)
             .await?
         else {
             unreachable!("unconditional turn construction must accept valid settings");
         };
-        Ok(turn)
+        Ok((turn_context, snapshot))
     }
 
     /// Commits accepted settings atomically, then constructs the turn without holding
@@ -808,7 +837,7 @@ impl Session {
         Ok(Some((turn_context, commit.snapshot)))
     }
 
-    /// Builds a turn from the exact committed settings without starting a task.
+    /// Constructs a turn from the exact committed settings without starting a task.
     async fn new_turn_from_configuration(
         &self,
         sub_id: String,
@@ -862,20 +891,12 @@ impl Session {
             .map(TurnEnvironment::permission_profile)
             .cloned()
             .unwrap_or_else(|| session_configuration.permission_profile());
-        let model_info = self
-            .services
-            .models_manager
-            .get_model_info(
-                session_configuration
-                    .step_settings
-                    .collaboration_mode
-                    .model(),
-                &session_configuration
-                    .model_info_overrides
-                    .models_manager_config(
-                        session_configuration.step_settings.personality,
-                        self.features.enabled(Feature::Personality),
-                    ),
+        let model_info = session_configuration
+            .step_settings
+            .resolve_model_info(
+                self.services.models_manager.as_ref(),
+                &session_configuration.model_info_overrides,
+                self.features.enabled(Feature::Personality),
             )
             .await;
         self.services
@@ -924,6 +945,11 @@ impl Session {
                 .snapshot_for_config(&skills_input, fs)
                 .await
         };
+        let step_settings = Arc::new(ResolvedStepSettings::new(
+            Arc::clone(&session_configuration.step_settings),
+            Arc::new(model_info),
+            self.features.enabled(Feature::FastMode),
+        ));
         let mut turn_context: TurnContext = Self::make_turn_context(
             self.thread_id(),
             self.session_id(),
@@ -936,7 +962,7 @@ impl Session {
             self.services.shell_zsh_path.as_ref(),
             self.services.main_execve_wrapper_exe.as_ref(),
             per_turn_config,
-            model_info,
+            step_settings,
             &self.services.models_manager,
             self.services
                 .network_proxy
@@ -973,13 +999,13 @@ impl Session {
     }
 
     pub(crate) async fn maybe_emit_model_warnings_for_turn(&self, tc: &TurnContext) {
-        if tc.model_info.used_fallback_model_metadata {
+        if tc.model_info().used_fallback_model_metadata {
             self.send_event(
                 tc,
                 EventMsg::Warning(WarningEvent {
                     message: format!(
                         "Model metadata for `{}` not found. Defaulting to fallback metadata; this can degrade performance and cause issues.",
-                        tc.model_info.slug
+                        tc.model_info().slug
                     ),
                 }),
             )
@@ -1002,7 +1028,7 @@ impl Session {
         }
 
         if let Some(message) =
-            unsupported_code_mode_warning(&tc.model_info, tc.config.features.get())
+            unsupported_code_mode_warning(tc.model_info(), tc.config.features.get())
         {
             self.send_event(tc, EventMsg::Warning(WarningEvent { message }))
                 .await;
diff --git a/codex-rs/core/src/session/turn_input.rs b/codex-rs/core/src/session/turn_input.rs
index 08ca3886bd..f0a34e2a27 100644
--- a/codex-rs/core/src/session/turn_input.rs
+++ b/codex-rs/core/src/session/turn_input.rs
@@ -130,7 +130,7 @@ impl PreparedTurnInputSettings {
         updates.final_output_json_schema = Some(final_output_json_schema);
         updates.service_tier_for_turn = service_tier;
 
-        let turn = match kind {
+        let turn_context = match kind {
             TurnStartKind::User | TurnStartKind::Recovery => Some(
                 session
                     .new_turn_with_sub_id(submission_id.clone(), updates)
@@ -144,7 +144,7 @@ impl PreparedTurnInputSettings {
                     .await?
             }
         };
-        let Some((turn_context, settings_snapshot)) = turn else {
+        let Some((turn_context, settings_snapshot)) = turn_context else {
             return Ok(None);
         };
         if emit_thread_settings_applied {
diff --git a/codex-rs/core/src/session/turn_input_tests.rs b/codex-rs/core/src/session/turn_input_tests.rs
index 06c1acf343..da374e176d 100644
--- a/codex-rs/core/src/session/turn_input_tests.rs
+++ b/codex-rs/core/src/session/turn_input_tests.rs
@@ -2,6 +2,7 @@ use super::*;
 use crate::config::Constrained;
 use crate::session::step_settings::StepSettingsUpdate;
 use crate::session::tests::make_session_and_context_with_rx;
+use crate::session::turn_context::TurnContext;
 use crate::state::TaskKind;
 use crate::tasks::SessionTask;
 use crate::tasks::SessionTaskResult;
@@ -126,7 +127,7 @@ async fn accepted_input_applies_thread_settings() {
             collaboration_mode: Some(CollaborationMode {
                 mode: ModeKind::Default,
                 settings: Settings {
-                    model: turn_context.model_info.slug.clone(),
+                    model: turn_context.model_info().slug.clone(),
                     reasoning_effort: config.model_reasoning_effort.clone(),
                     developer_instructions: None,
                 },
@@ -382,6 +383,14 @@ async fn prepared_user_updates_merge_with_settings_at_turn_start() {
         );
         assert_eq!(session.collaboration_mode().await, expected);
         assert_eq!(turn_context.collaboration_mode(), expected);
+        assert_eq!(
+            turn_context.initial_settings.selected_collaboration_mode(),
+            &expected
+        );
+        assert!(Arc::ptr_eq(
+            &turn_context.initial_settings.model_info,
+            turn_context.model_info(),
+        ));
     }
 }
 
@@ -432,6 +441,10 @@ async fn automatic_admission_uses_current_candidate_after_plan_preview() {
     );
     assert_eq!(session.collaboration_mode().await, expected);
     assert_eq!(turn_context.collaboration_mode(), expected);
+    assert_eq!(
+        turn_context.initial_settings.selected_collaboration_mode(),
+        &expected
+    );
 }
 
 #[tokio::test]
diff --git a/codex-rs/core/src/session/world_state.rs b/codex-rs/core/src/session/world_state.rs
index 2baaf8768d..ca21831c1e 100644
--- a/codex-rs/core/src/session/world_state.rs
+++ b/codex-rs/core/src/session/world_state.rs
@@ -41,8 +41,8 @@ impl Session {
             "building step world state"
         );
         let model_instructions = turn_context
-            .model_info
-            .get_model_instructions(turn_context.personality);
+            .model_info()
+            .get_model_instructions(turn_context.personality());
         let (previous_model, previous_context, base_instructions) = {
             let state = self.state.lock().await;
             let base_instructions = state.session_configuration.base_instructions.clone();
@@ -65,7 +65,7 @@ impl Session {
                 base_instructions,
             )
         };
-        let personality_is_baked = turn_context.model_info.supports_personality()
+        let personality_is_baked = turn_context.model_info().supports_personality()
             && base_instructions == model_instructions;
         let environment_subagents = if turn_context.config.include_environment_context {
             self.services
@@ -77,22 +77,22 @@ impl Session {
         };
         let mut world_state = WorldState::default();
         world_state.add_section(ModelInstructionsState::new(
-            &turn_context.model_info.slug,
+            &turn_context.model_info().slug,
             previous_model.as_deref(),
             model_instructions,
         ));
         if self.features.enabled(Feature::Personality) {
-            let personality_instructions = turn_context.personality.and_then(|personality| {
+            let personality_instructions = turn_context.personality().and_then(|personality| {
                 turn_context
-                    .model_info
+                    .model_info()
                     .model_messages
                     .as_ref()
                     .and_then(|messages| messages.get_personality_message(Some(personality)))
                     .filter(|message| !message.is_empty())
             });
             world_state.add_section(PersonalityState::new(
-                &turn_context.model_info.slug,
-                turn_context.personality,
+                &turn_context.model_info().slug,
+                turn_context.personality(),
                 previous_context
                     .as_ref()
                     .map(|previous| previous.model.as_str())
@@ -156,12 +156,12 @@ impl Session {
             let cwd = environment
                 .and_then(|environment| environment.cwd().to_abs_path().ok())
                 .unwrap_or_else(|| turn_context.cwd.clone());
-            let model_messages = turn_context.model_info.model_messages.as_ref();
+            let model_messages = turn_context.model_info().model_messages.as_ref();
             world_state.add_section(PermissionsState::new(
                 &permission_profile,
-                step_context.approval_policy,
+                step_context.settings.approval_policy(),
                 ApprovalPromptContext::new(
-                    step_context.approvals_reviewer,
+                    step_context.settings.approvals_reviewer(),
                     model_messages.and_then(|messages| messages.approvals.as_ref()),
                     model_messages.and_then(|messages| messages.permissions.as_ref()),
                 ),
@@ -183,7 +183,7 @@ impl Session {
             world_state.add_section(CollaborationModeState::from_collaboration_mode(
                 &turn_context.collaboration_mode(),
                 turn_context
-                    .model_info
+                    .model_info()
                     .model_messages
                     .as_ref()
                     .and_then(|messages| messages.collaboration_modes.as_ref()),
@@ -227,12 +227,12 @@ impl Session {
                 false
             };
         let apps_usage_instructions_available =
-            apps_available && turn_context.model_info.include_apps_usage_instructions;
+            apps_available && turn_context.model_info().include_apps_usage_instructions;
         world_state.add_section(AppsInstructionsState::new(
             apps_usage_instructions_available,
         ));
         let plugins_usage_instructions_available = step_context.mcp.plugins_available()
-            && turn_context.model_info.include_plugin_usage_instructions;
+            && turn_context.model_info().include_plugin_usage_instructions;
         world_state.add_section(PluginsInstructionsState::new(
             plugins_usage_instructions_available,
         ));
diff --git a/codex-rs/core/src/session_startup_prewarm.rs b/codex-rs/core/src/session_startup_prewarm.rs
index 4d63cc8c77..4ae1af8b85 100644
--- a/codex-rs/core/src/session_startup_prewarm.rs
+++ b/codex-rs/core/src/session_startup_prewarm.rs
@@ -314,11 +314,11 @@ async fn schedule_startup_prewarm_inner(
     client_session
         .prewarm_websocket(
             &startup_prompt,
-            &step_context.model_info,
+            &step_context.settings.model_info,
             &step_context.session_telemetry,
-            step_context.reasoning_effort.clone(),
-            step_context.reasoning_summary,
-            step_context.service_tier.clone(),
+            step_context.settings.reasoning_effort().cloned(),
+            step_context.settings.reasoning_summary,
+            step_context.settings.service_tier.clone(),
             &responses_metadata,
         )
         .await?;
diff --git a/codex-rs/core/src/skills.rs b/codex-rs/core/src/skills.rs
index abe8f46674..4d35dd403a 100644
--- a/codex-rs/core/src/skills.rs
+++ b/codex-rs/core/src/skills.rs
@@ -150,7 +150,7 @@ pub(crate) async fn maybe_emit_implicit_skill_invocation(
         .analytics_events_client
         .track_skill_invocations(
             build_track_events_context(
-                turn_context.model_info.slug.clone(),
+                turn_context.model_info().slug.clone(),
                 sess.thread_id.to_string(),
                 turn_context.sub_id.clone(),
                 turn_context.originator.clone(),
diff --git a/codex-rs/core/src/stream_events_utils.rs b/codex-rs/core/src/stream_events_utils.rs
index 53afbf1d7e..5445313656 100644
--- a/codex-rs/core/src/stream_events_utils.rs
+++ b/codex-rs/core/src/stream_events_utils.rs
@@ -100,7 +100,7 @@ pub(crate) async fn record_completed_response_item_with_finalized_facts(
         || {
             completed_item_defers_mailbox_delivery_to_next_turn(
                 item,
-                turn_context.mode == ModeKind::Plan,
+                turn_context.mode() == ModeKind::Plan,
             )
         },
         |facts| facts.defers_mailbox_delivery_to_next_turn,
@@ -292,7 +292,7 @@ pub(crate) async fn handle_output_item_done(
     previously_active_item: Option<TurnItem>,
 ) -> Result<OutputItemResult> {
     let mut output = OutputItemResult::default();
-    let plan_mode = ctx.turn_context.mode == ModeKind::Plan;
+    let plan_mode = ctx.turn_context.mode() == ModeKind::Plan;
 
     match ToolRouter::build_tool_call(item.clone()) {
         // The model emitted a tool call; log it, persist the item immediately, and queue the tool execution.
diff --git a/codex-rs/core/src/tasks/mod.rs b/codex-rs/core/src/tasks/mod.rs
index f8fae7e986..87ee5a12f1 100644
--- a/codex-rs/core/src/tasks/mod.rs
+++ b/codex-rs/core/src/tasks/mod.rs
@@ -375,7 +375,7 @@ impl Session {
             otel.name = span_name,
             thread.id = %self.thread_id,
             turn.id = %turn_context.sub_id,
-            model = %turn_context.model_info.slug,
+            model = %turn_context.model_info().slug,
             codex.turn.reasoning_effort = %reasoning_effort,
             codex.turn.token_usage.input_tokens = field::Empty,
             codex.turn.token_usage.cached_input_tokens = field::Empty,
diff --git a/codex-rs/core/src/tasks/regular.rs b/codex-rs/core/src/tasks/regular.rs
index e7b4166149..7b999967c3 100644
--- a/codex-rs/core/src/tasks/regular.rs
+++ b/codex-rs/core/src/tasks/regular.rs
@@ -52,7 +52,7 @@ impl SessionTask for RegularTask {
                 trace_id: ctx.trace_id.clone(),
                 started_at: ctx.turn_timing_state.started_at_unix_secs().await,
                 model_context_window: ctx.model_context_window(),
-                collaboration_mode_kind: ctx.mode,
+                collaboration_mode_kind: ctx.mode(),
             });
             sess.send_event(ctx.as_ref(), event).await;
             sess.set_server_reasoning_included(/*included*/ false).await;
diff --git a/codex-rs/core/src/tasks/review.rs b/codex-rs/core/src/tasks/review.rs
index 94859375dd..2369495996 100644
--- a/codex-rs/core/src/tasks/review.rs
+++ b/codex-rs/core/src/tasks/review.rs
@@ -121,7 +121,7 @@ async fn start_review_conversation(
     let model = config
         .review_model
         .clone()
-        .unwrap_or_else(|| ctx.model_info.slug.clone());
+        .unwrap_or_else(|| ctx.model_info().slug.clone());
     sub_agent_config.model = Some(model);
     (run_codex_thread_one_shot(
         sub_agent_config,
diff --git a/codex-rs/core/src/tasks/user_shell.rs b/codex-rs/core/src/tasks/user_shell.rs
index 7b55a58fc0..1b308b2c16 100644
--- a/codex-rs/core/src/tasks/user_shell.rs
+++ b/codex-rs/core/src/tasks/user_shell.rs
@@ -122,7 +122,7 @@ pub(crate) async fn execute_user_shell_command(
             trace_id: turn_context.trace_id.clone(),
             started_at: turn_context.turn_timing_state.started_at_unix_secs().await,
             model_context_window: turn_context.model_context_window(),
-            collaboration_mode_kind: turn_context.mode,
+            collaboration_mode_kind: turn_context.mode(),
         });
         session.send_event(turn_context.as_ref(), event).await;
     }
@@ -312,7 +312,7 @@ pub(crate) async fn execute_user_shell_command(
                         duration: Some(output.duration),
                         formatted_output: Some(format_exec_output_str(
                             &output,
-                            turn_context.model_info.truncation_policy.into(),
+                            turn_context.model_info().truncation_policy.into(),
                         )),
                     }),
                 )
@@ -353,7 +353,7 @@ pub(crate) async fn execute_user_shell_command(
                         duration: Some(exec_output.duration),
                         formatted_output: Some(format_exec_output_str(
                             &exec_output,
-                            turn_context.model_info.truncation_policy.into(),
+                            turn_context.model_info().truncation_policy.into(),
                         )),
                     }),
                 )
diff --git a/codex-rs/core/src/thread_manager_tests.rs b/codex-rs/core/src/thread_manager_tests.rs
index 41728a6684..87878eab23 100644
--- a/codex-rs/core/src/thread_manager_tests.rs
+++ b/codex-rs/core/src/thread_manager_tests.rs
@@ -1561,12 +1561,13 @@ async fn resume_and_fork_do_not_restore_thread_environments_from_rollout() {
         )
         .await
         .expect("resume source thread");
-    let (resumed_turn, _) = resumed
+    let (prepared_turn, _) = resumed
         .thread
         .session
         .new_turn_with_sub_id("resume-turn".to_string(), SessionSettingsUpdate::default())
         .await
         .expect("build resumed turn context");
+    let resumed_turn = prepared_turn;
     assert_eq!(resumed_turn.environments.turn_environments().count(), 1);
     assert_eq!(
         resumed_turn
@@ -1595,12 +1596,13 @@ async fn resume_and_fork_do_not_restore_thread_environments_from_rollout() {
         )
         .await
         .expect("fork source thread");
-    let (forked_turn, _) = forked
+    let (prepared_turn, _) = forked
         .thread
         .session
         .new_turn_with_sub_id("fork-turn".to_string(), SessionSettingsUpdate::default())
         .await
         .expect("build forked turn context");
+    let forked_turn = prepared_turn;
     assert_eq!(forked_turn.environments.turn_environments().count(), 1);
     assert_eq!(
         forked_turn
diff --git a/codex-rs/core/src/tools/approvals.rs b/codex-rs/core/src/tools/approvals.rs
index ce939f37b1..d78e14f102 100644
--- a/codex-rs/core/src/tools/approvals.rs
+++ b/codex-rs/core/src/tools/approvals.rs
@@ -497,7 +497,7 @@ impl Session {
                 _ => {}
             }
         }
-        resolution.into_tool_result(&ctx.review_context.turn().model_info)
+        resolution.into_tool_result(ctx.review_context.turn().model_info())
     }
 
     async fn request_reviewer_approval(
diff --git a/codex-rs/core/src/tools/code_mode/mod.rs b/codex-rs/core/src/tools/code_mode/mod.rs
index 0ce1e66b9c..94e9ce7c1b 100644
--- a/codex-rs/core/src/tools/code_mode/mod.rs
+++ b/codex-rs/core/src/tools/code_mode/mod.rs
@@ -277,7 +277,7 @@ pub(super) async fn handle_runtime_response(
 }
 
 fn sanitize_runtime_image_detail(turn: &TurnContext, items: &mut [FunctionCallOutputContentItem]) {
-    sanitize_image_detail_items(can_request_original_image_detail(&turn.model_info), items);
+    sanitize_image_detail_items(can_request_original_image_detail(turn.model_info()), items);
 }
 
 fn format_script_status(response: &RuntimeResponse) -> String {
diff --git a/codex-rs/core/src/tools/events.rs b/codex-rs/core/src/tools/events.rs
index 5921000fe2..5fa91cc82c 100644
--- a/codex-rs/core/src/tools/events.rs
+++ b/codex-rs/core/src/tools/events.rs
@@ -132,7 +132,7 @@ async fn emit_exec_command_begin(ctx: ToolEventCtx<'_>, exec_input: &ExecCommand
             .analytics_events_client
             .track_artifact_operation(
                 build_track_events_context(
-                    ctx.turn.model_info.slug.clone(),
+                    ctx.turn.model_info().slug.clone(),
                     ctx.session.thread_id.to_string(),
                     ctx.turn.sub_id.clone(),
                     ctx.turn.originator.clone(),
@@ -373,7 +373,7 @@ impl ToolEmitter {
         output: &ExecToolCallOutput,
         ctx: ToolEventCtx<'_>,
     ) -> String {
-        super::format_exec_output_for_model(output, ctx.turn.model_info.truncation_policy.into())
+        super::format_exec_output_for_model(output, ctx.turn.model_info().truncation_policy.into())
     }
 
     pub async fn finish(
@@ -521,7 +521,7 @@ async fn emit_exec_stage(
                 duration: output.duration,
                 formatted_output: format_exec_output_str(
                     &output,
-                    ctx.turn.model_info.truncation_policy.into(),
+                    ctx.turn.model_info().truncation_policy.into(),
                 ),
                 status: if output.exit_code == 0 {
                     ExecCommandStatus::Completed
diff --git a/codex-rs/core/src/tools/handlers/extension_tools.rs b/codex-rs/core/src/tools/handlers/extension_tools.rs
index ec825c774e..cdd068d0ac 100644
--- a/codex-rs/core/src/tools/handlers/extension_tools.rs
+++ b/codex-rs/core/src/tools/handlers/extension_tools.rs
@@ -162,7 +162,7 @@ async fn to_extension_call(invocation: &ToolInvocation) -> ExtensionToolCall {
         .turn
         .turn_metadata_state
         .current_meta_value_for_mcp_request(McpTurnMetadataContext {
-            model: invocation.turn.model_info.slug.as_str(),
+            model: invocation.turn.model_info().slug.as_str(),
             reasoning_effort: invocation.turn.effective_reasoning_effort(),
         })
         .and_then(|metadata| to_ascii_json_string(&metadata).ok());
@@ -194,9 +194,9 @@ async fn to_extension_call(invocation: &ToolInvocation) -> ExtensionToolCall {
         turn_id: invocation.turn.sub_id.clone(),
         call_id: invocation.call_id.clone(),
         tool_name: invocation.tool_name.clone(),
-        model: invocation.turn.model_info.slug.clone(),
+        model: invocation.turn.model_info().slug.clone(),
         codex_turn_metadata,
-        truncation_policy: invocation.turn.model_info.truncation_policy.into(),
+        truncation_policy: invocation.turn.model_info().truncation_policy.into(),
         source: extension_tool_call_source(invocation.source.clone()),
         conversation_history,
         turn_item_emitter: Arc::new(CoreTurnItemEmitter {
@@ -388,8 +388,8 @@ mod tests {
         let weak_session = Arc::downgrade(&session);
         let weak_turn = Arc::downgrade(&turn);
         let turn_id = turn.sub_id.clone();
-        let model = turn.model_info.slug.clone();
-        let truncation_policy = turn.model_info.truncation_policy.into();
+        let model = turn.model_info().slug.clone();
+        let truncation_policy = turn.model_info().truncation_policy.into();
         let expected_sandbox_cwds = turn
             .environments
             .turn_environments()
diff --git a/codex-rs/core/src/tools/handlers/mcp.rs b/codex-rs/core/src/tools/handlers/mcp.rs
index 5cead01f3d..b62945b1f9 100644
--- a/codex-rs/core/src/tools/handlers/mcp.rs
+++ b/codex-rs/core/src/tools/handlers/mcp.rs
@@ -208,8 +208,8 @@ impl McpHandler {
             result: result.result,
             tool_input: result.tool_input,
             wall_time: started.elapsed(),
-            original_image_detail_supported: can_request_original_image_detail(&turn.model_info),
-            truncation_policy: turn.model_info.truncation_policy.into(),
+            original_image_detail_supported: can_request_original_image_detail(turn.model_info()),
+            truncation_policy: turn.model_info().truncation_policy.into(),
         }))
     }
 }
diff --git a/codex-rs/core/src/tools/handlers/mcp_resource.rs b/codex-rs/core/src/tools/handlers/mcp_resource.rs
index deb7491e75..5e18ee448f 100644
--- a/codex-rs/core/src/tools/handlers/mcp_resource.rs
+++ b/codex-rs/core/src/tools/handlers/mcp_resource.rs
@@ -290,7 +290,7 @@ where
     emit_tool_call_begin(session, turn, call_id, invocation.clone()).await;
     let start = Instant::now();
     let result = operation.await.and_then(|payload| {
-        serialize_function_output(payload, turn.model_info.truncation_policy.into())
+        serialize_function_output(payload, turn.model_info().truncation_policy.into())
     });
 
     match result {
diff --git a/codex-rs/core/src/tools/handlers/multi_agents_common.rs b/codex-rs/core/src/tools/handlers/multi_agents_common.rs
index 843030b274..9fdfd48962 100644
--- a/codex-rs/core/src/tools/handlers/multi_agents_common.rs
+++ b/codex-rs/core/src/tools/handlers/multi_agents_common.rs
@@ -194,13 +194,13 @@ pub(crate) fn build_agent_resume_config(turn: &TurnContext) -> Result<Config, Fu
 fn build_agent_shared_config(turn: &TurnContext) -> Result<Config, FunctionCallError> {
     let base_config = turn.config.clone();
     let mut config = (*base_config).clone();
-    config.model = Some(turn.model_info.slug.clone());
+    config.model = Some(turn.model_info().slug.clone());
     config.model_provider = turn.provider.info().clone();
     config.model_reasoning_effort = turn
-        .reasoning_effort
-        .clone()
-        .or_else(|| turn.model_info.default_reasoning_level.clone());
-    config.model_reasoning_summary = Some(turn.reasoning_summary);
+        .reasoning_effort()
+        .or(turn.model_info().default_reasoning_level.as_ref())
+        .cloned();
+    config.model_reasoning_summary = Some(turn.reasoning_summary());
     config.developer_instructions = turn.developer_instructions.clone();
     if turn.multi_agent_version == MultiAgentVersion::V2
         && let Some(developer_instructions) = turn
@@ -308,8 +308,8 @@ pub(crate) async fn apply_requested_spawn_agent_model_overrides(
 
     if let Some(reasoning_effort) = requested_reasoning_effort {
         validate_spawn_agent_reasoning_effort(
-            &turn.model_info.slug,
-            &turn.model_info.supported_reasoning_levels,
+            &turn.model_info().slug,
+            &turn.model_info().supported_reasoning_levels,
             &reasoning_effort,
         )?;
         config.model_reasoning_effort = Some(reasoning_effort);
diff --git a/codex-rs/core/src/tools/handlers/multi_agents_tests.rs b/codex-rs/core/src/tools/handlers/multi_agents_tests.rs
index fc76ab4b47..d364236b07 100644
--- a/codex-rs/core/src/tools/handlers/multi_agents_tests.rs
+++ b/codex-rs/core/src/tools/handlers/multi_agents_tests.rs
@@ -386,11 +386,9 @@ async fn multi_agent_v2_spawn_fork_turns_all_applies_agent_type_override() {
         .features
         .enable(Feature::MultiAgentV2)
         .expect("test config should allow feature update");
-    let turn = TurnContext {
-        config: Arc::new(config),
-        multi_agent_version: codex_protocol::protocol::MultiAgentVersion::V2,
-        ..turn
-    };
+    let mut turn = turn;
+    turn.config = Arc::new(config);
+    turn.multi_agent_version = codex_protocol::protocol::MultiAgentVersion::V2;
 
     SpawnAgentHandlerV2::default()
         .handle(invocation(
@@ -915,11 +913,9 @@ async fn multi_agent_v2_spawn_partial_fork_turns_allows_agent_type_override() {
         .features
         .enable(Feature::MultiAgentV2)
         .expect("test config should allow feature update");
-    let turn = TurnContext {
-        config: Arc::new(config),
-        multi_agent_version: codex_protocol::protocol::MultiAgentVersion::V2,
-        ..turn
-    };
+    let mut turn = turn;
+    turn.config = Arc::new(config);
+    turn.multi_agent_version = codex_protocol::protocol::MultiAgentVersion::V2;
     let parent_provider_id = turn.config.model_provider_id.clone();
 
     let output = SpawnAgentHandlerV2::default()
@@ -4534,7 +4530,7 @@ async fn build_agent_spawn_config_uses_turn_context_values() {
     let base_instructions = BaseInstructions {
         text: "base".to_string(),
         provenance: Some(BaseInstructionsProvenance::Model {
-            model: turn.model_info.slug.clone(),
+            model: turn.model_info().slug.clone(),
         }),
     };
     turn.developer_instructions = Some("dev".to_string());
@@ -4581,10 +4577,10 @@ async fn build_agent_spawn_config_uses_turn_context_values() {
     let mut expected = (*turn.config).clone();
     expected.base_instructions_provenance = base_instructions.provenance.clone();
     expected.base_instructions = Some(base_instructions.text);
-    expected.model = Some(turn.model_info.slug.clone());
+    expected.model = Some(turn.model_info().slug.clone());
     expected.model_provider = turn.provider.info().clone();
-    expected.model_reasoning_effort = turn.reasoning_effort.clone();
-    expected.model_reasoning_summary = Some(turn.reasoning_summary);
+    expected.model_reasoning_effort = turn.reasoning_effort().cloned();
+    expected.model_reasoning_summary = Some(turn.reasoning_summary());
     expected.developer_instructions = turn.developer_instructions.clone();
     #[allow(deprecated)]
     {
@@ -4604,7 +4600,7 @@ async fn build_agent_resume_config_clears_base_instructions() {
     let mut base_config = (*turn.config).clone();
     base_config.base_instructions = Some("caller-base".to_string());
     base_config.base_instructions_provenance = Some(BaseInstructionsProvenance::Model {
-        model: turn.model_info.slug.clone(),
+        model: turn.model_info().slug.clone(),
     });
     turn.config = Arc::new(base_config);
     Arc::make_mut(&mut turn.config)
@@ -4634,10 +4630,10 @@ async fn build_agent_resume_config_clears_base_instructions() {
     let mut expected = (*turn.config).clone();
     expected.base_instructions = None;
     expected.base_instructions_provenance = None;
-    expected.model = Some(turn.model_info.slug.clone());
+    expected.model = Some(turn.model_info().slug.clone());
     expected.model_provider = turn.provider.info().clone();
-    expected.model_reasoning_effort = turn.reasoning_effort.clone();
-    expected.model_reasoning_summary = Some(turn.reasoning_summary);
+    expected.model_reasoning_effort = turn.reasoning_effort().cloned();
+    expected.model_reasoning_summary = Some(turn.reasoning_summary());
     expected.developer_instructions = turn.developer_instructions.clone();
     #[allow(deprecated)]
     {
diff --git a/codex-rs/core/src/tools/handlers/multi_agents_v2/spawn.rs b/codex-rs/core/src/tools/handlers/multi_agents_v2/spawn.rs
index 394d0a57e9..f783f23405 100644
--- a/codex-rs/core/src/tools/handlers/multi_agents_v2/spawn.rs
+++ b/codex-rs/core/src/tools/handlers/multi_agents_v2/spawn.rs
@@ -186,7 +186,7 @@ async fn handle_spawn_agent(
     let multi_agent_v2_usage_hints =
         if is_full_history_fork && turn.multi_agent_version == MultiAgentVersion::V2 {
             let child_model_info = match config.model.as_deref() {
-                Some(model) if model != turn.model_info.slug => Some(
+                Some(model) if model != turn.model_info().slug => Some(
                     session
                         .services
                         .models_manager
@@ -197,7 +197,7 @@ async fn handle_spawn_agent(
             };
             let child_catalog = child_model_info
                 .as_ref()
-                .unwrap_or(&turn.model_info)
+                .unwrap_or(turn.model_info())
                 .model_messages
                 .as_ref()
                 .and_then(|messages| messages.multi_agent.as_ref())
diff --git a/codex-rs/core/src/tools/handlers/plan.rs b/codex-rs/core/src/tools/handlers/plan.rs
index 2c21334a3f..7fdd1fb4a3 100644
--- a/codex-rs/core/src/tools/handlers/plan.rs
+++ b/codex-rs/core/src/tools/handlers/plan.rs
@@ -81,7 +81,7 @@ impl PlanHandler {
             }
         };
 
-        if turn.mode == ModeKind::Plan {
+        if turn.mode() == ModeKind::Plan {
             return Err(FunctionCallError::RespondToModel(
                 "update_plan is a TODO/checklist tool and is not allowed in Plan mode".to_string(),
             ));
diff --git a/codex-rs/core/src/tools/handlers/request_plugin_install.rs b/codex-rs/core/src/tools/handlers/request_plugin_install.rs
index 02dcebc54d..25348720ac 100644
--- a/codex-rs/core/src/tools/handlers/request_plugin_install.rs
+++ b/codex-rs/core/src/tools/handlers/request_plugin_install.rs
@@ -217,7 +217,7 @@ impl RequestPluginInstallHandler {
                 .analytics_events_client
                 .track_plugin_install_requested(
                     build_track_events_context(
-                        turn.model_info.slug.clone(),
+                        turn.model_info().slug.clone(),
                         session.thread_id.to_string(),
                         turn.sub_id.clone(),
                         turn.originator.clone(),
diff --git a/codex-rs/core/src/tools/handlers/request_user_input_tests.rs b/codex-rs/core/src/tools/handlers/request_user_input_tests.rs
index dec9884e51..d6cc5ffc1a 100644
--- a/codex-rs/core/src/tools/handlers/request_user_input_tests.rs
+++ b/codex-rs/core/src/tools/handlers/request_user_input_tests.rs
@@ -2,6 +2,8 @@ use super::*;
 use crate::session::step_context::StepContext;
 use crate::session::tests::make_session_and_context;
 use crate::session::tests::make_session_and_context_with_rx;
+use crate::session::tests::update_selected_settings_for_test;
+use crate::session::tests::update_turn_settings_for_test;
 use crate::state::ActiveTurn;
 use crate::tools::context::ToolInvocation;
 use crate::tools::context::ToolPayload;
@@ -224,9 +226,14 @@ async fn guardian_user_input_evidence_is_bounded() {
 #[tokio::test]
 async fn request_user_input_sets_blocking_from_turn_mode() {
     let (session, mut turn, events) = make_session_and_context_with_rx().await;
-    Arc::get_mut(&mut turn)
-        .expect("turn context should be uniquely owned")
-        .mode = ModeKind::Plan;
+    update_turn_settings_for_test(
+        Arc::get_mut(&mut turn).expect("turn context should be uniquely owned"),
+        |settings| {
+            update_selected_settings_for_test(settings, |selected| {
+                selected.collaboration_mode.mode = ModeKind::Plan;
+            });
+        },
+    );
     *session.active_turn.lock().await = Some(ActiveTurn::default());
 
     let request = tokio::spawn({
diff --git a/codex-rs/core/src/tools/handlers/unified_exec/exec_command.rs b/codex-rs/core/src/tools/handlers/unified_exec/exec_command.rs
index 9c6c17c43b..f0bf1de790 100644
--- a/codex-rs/core/src/tools/handlers/unified_exec/exec_command.rs
+++ b/codex-rs/core/src/tools/handlers/unified_exec/exec_command.rs
@@ -345,7 +345,7 @@ impl ExecCommandHandler {
                 chunk_id: String::new(),
                 wall_time: std::time::Duration::ZERO,
                 raw_output: output.into_text().into_bytes(),
-                truncation_policy: turn.model_info.truncation_policy.into(),
+                truncation_policy: turn.model_info().truncation_policy.into(),
                 max_output_tokens,
                 process_id: None,
                 exit_code: None,
@@ -397,7 +397,7 @@ impl ExecCommandHandler {
                     chunk_id: generate_chunk_id(),
                     wall_time: output.duration,
                     raw_output: output_text.into_bytes(),
-                    truncation_policy: turn.model_info.truncation_policy.into(),
+                    truncation_policy: turn.model_info().truncation_policy.into(),
                     max_output_tokens,
                     // Sandbox denial is terminal, so there is no live
                     // process for write_stdin to resume.
diff --git a/codex-rs/core/src/tools/handlers/unified_exec/write_stdin.rs b/codex-rs/core/src/tools/handlers/unified_exec/write_stdin.rs
index 7f1709b045..23be88be68 100644
--- a/codex-rs/core/src/tools/handlers/unified_exec/write_stdin.rs
+++ b/codex-rs/core/src/tools/handlers/unified_exec/write_stdin.rs
@@ -78,7 +78,7 @@ impl WriteStdinHandler {
                 input: &args.chars,
                 yield_time_ms: args.yield_time_ms,
                 max_output_tokens: args.max_output_tokens,
-                truncation_policy: turn.model_info.truncation_policy.into(),
+                truncation_policy: turn.model_info().truncation_policy.into(),
                 interaction_event: Some(WriteStdinInteractionEvent {
                     session: &session,
                     turn: &turn,
diff --git a/codex-rs/core/src/tools/handlers/view_image.rs b/codex-rs/core/src/tools/handlers/view_image.rs
index aa47ddd359..8e7054fb7d 100644
--- a/codex-rs/core/src/tools/handlers/view_image.rs
+++ b/codex-rs/core/src/tools/handlers/view_image.rs
@@ -93,7 +93,7 @@ impl ViewImageHandler {
     ) -> Result<Box<dyn crate::tools::context::ToolOutput>, FunctionCallError> {
         if !invocation
             .turn
-            .model_info
+            .model_info()
             .input_modalities
             .contains(&InputModality::Image)
         {
@@ -182,7 +182,7 @@ impl ViewImageHandler {
             FunctionCallError::RespondToModel(VIEW_IMAGE_INVALID_MESSAGE.to_string())
         })?;
 
-        let can_request_original_detail = can_request_original_image_detail(&turn.model_info);
+        let can_request_original_detail = can_request_original_image_detail(turn.model_info());
         let use_original_detail = self.options.unified_image_budget
             || can_request_original_detail && matches!(detail, Some(ViewImageDetail::Original));
         let image_detail = if use_original_detail {
diff --git a/codex-rs/core/src/tools/mod.rs b/codex-rs/core/src/tools/mod.rs
index df6b5969a3..e262e00cf0 100644
--- a/codex-rs/core/src/tools/mod.rs
+++ b/codex-rs/core/src/tools/mod.rs
@@ -65,7 +65,7 @@ pub(crate) fn tool_user_shell_type(
 }
 
 pub(crate) fn requested_tool_mode(turn_context: &TurnContext) -> ToolMode {
-    turn_context.model_info.tool_mode.unwrap_or_else(|| {
+    turn_context.model_info().tool_mode.unwrap_or_else(|| {
         if turn_context.config.features.enabled(Feature::CodeModeOnly) {
             ToolMode::CodeModeOnly
         } else if turn_context.config.features.enabled(Feature::CodeMode) {
diff --git a/codex-rs/core/src/tools/runtimes/zsh_fork/unix_escalation.rs b/codex-rs/core/src/tools/runtimes/zsh_fork/unix_escalation.rs
index 87f8521cfd..7eb07228b7 100644
--- a/codex-rs/core/src/tools/runtimes/zsh_fork/unix_escalation.rs
+++ b/codex-rs/core/src/tools/runtimes/zsh_fork/unix_escalation.rs
@@ -365,7 +365,7 @@ impl CoreShellActionProvider {
                         }
                         ReviewDecision::TimedOut => EscalationDecision::deny(Some(
                             crate::guardian::guardian_timeout_message(
-                                &self.review_context.turn().model_info,
+                                self.review_context.turn().model_info(),
                             ),
                         )),
                         ReviewDecision::ApprovedMcpPolicyAmendment => {
diff --git a/codex-rs/core/src/tools/spec_plan.rs b/codex-rs/core/src/tools/spec_plan.rs
index b317ca2c02..e159828c63 100644
--- a/codex-rs/core/src/tools/spec_plan.rs
+++ b/codex-rs/core/src/tools/spec_plan.rs
@@ -373,7 +373,7 @@ pub(crate) fn finalize_tool_router(
         .config
         .tool_registry
         .turn_metadata_includes_tool_info
-        && turn_context.model_info.use_responses_lite;
+        && turn_context.model_info().use_responses_lite;
 
     if turn_context.config.tool_registry.error_on_tool_collisions {
         if let Some(tool_name) = registry.first_collision() {
@@ -547,7 +547,7 @@ fn hosted_model_tool_specs(
     registered_extension_tool_names: &[ToolName],
 ) -> Vec<ToolSpec> {
     // Responses Lite accepts schemas for client-executed tools, not hosted Responses tools.
-    if turn_context.model_info.use_responses_lite
+    if turn_context.model_info().use_responses_lite
         || crate::guardian::is_basic_session_source(&turn_context.session_source)
     {
         return Vec::new();
@@ -567,7 +567,7 @@ fn hosted_model_tool_specs(
     if let Some(hosted_web_search_tool) = create_web_search_tool(WebSearchToolOptions {
         web_search_mode,
         web_search_config,
-        web_search_tool_type: turn_context.model_info.web_search_tool_type,
+        web_search_tool_type: turn_context.model_info().web_search_tool_type,
     }) {
         specs.push(hosted_web_search_tool);
     }
@@ -575,7 +575,7 @@ fn hosted_model_tool_specs(
 }
 
 pub(crate) fn search_tool_enabled(turn_context: &TurnContext) -> bool {
-    turn_context.model_info.supports_search_tool && namespace_tools_enabled(turn_context)
+    turn_context.model_info().supports_search_tool && namespace_tools_enabled(turn_context)
 }
 
 pub(crate) fn tool_suggest_enabled(turn_context: &TurnContext) -> bool {
@@ -602,7 +602,7 @@ fn collab_tools_enabled(turn_context: &TurnContext) -> bool {
         ),
         MultiAgentVersion::V2 => {
             turn_context.session_source.get_agent_path().is_none()
-                || turn_context.model_info.multi_agent_version == Some(MultiAgentVersion::V2)
+                || turn_context.model_info().multi_agent_version == Some(MultiAgentVersion::V2)
         }
     }
 }
@@ -633,7 +633,7 @@ fn image_generation_available(turn_context: &TurnContext) -> bool {
     }
 
     if !turn_context
-        .model_info
+        .model_info()
         .input_modalities
         .contains(&InputModality::Image)
     {
@@ -794,8 +794,10 @@ fn register_code_mode_executors(
             &namespace_descriptions,
             turn_context.config.code_mode.default_exec_yield_time_ms,
             tool_mode == ToolMode::CodeModeOnly,
-            if unified_image_budget_enabled(&turn_context.config.features, &turn_context.model_info)
-            {
+            if unified_image_budget_enabled(
+                &turn_context.config.features,
+                turn_context.model_info(),
+            ) {
                 codex_code_mode::ImageDetailVisibility::Hidden
             } else {
                 codex_code_mode::ImageDetailVisibility::Visible
@@ -908,7 +910,7 @@ fn add_core_tool_sources(context: &CoreToolPlanContext<'_>, registry: &mut ToolR
             if turn_context.config.features.enabled(Feature::ShellTool)
                 && turn_context.config.features.enabled(Feature::UnifiedExec)
                 && !matches!(
-                    turn_context.model_info.shell_type,
+                    turn_context.model_info().shell_type,
                     ConfigShellToolType::Disabled
                 )
             {
@@ -926,11 +928,11 @@ fn add_core_tool_sources(context: &CoreToolPlanContext<'_>, registry: &mut ToolR
             if turn_context.config.features.enabled(Feature::ViewImage) {
                 registry.add(ViewImageHandler::new(ViewImageToolOptions {
                     can_request_original_image_detail: can_request_original_image_detail(
-                        &turn_context.model_info,
+                        turn_context.model_info(),
                     ),
                     unified_image_budget: unified_image_budget_enabled(
                         &turn_context.config.features,
-                        &turn_context.model_info,
+                        turn_context.model_info(),
                     ),
                     include_environment_id,
                 }));
@@ -948,7 +950,7 @@ fn add_core_tool_sources(context: &CoreToolPlanContext<'_>, registry: &mut ToolR
 fn standalone_web_search_enabled(turn_context: &TurnContext) -> bool {
     namespace_tools_enabled(turn_context)
         && turn_context.provider.capabilities().web_search
-        && (turn_context.model_info.use_responses_lite
+        && (turn_context.model_info().use_responses_lite
             || turn_context
                 .config
                 .features
@@ -975,7 +977,7 @@ fn add_shell_tools(context: &CoreToolPlanContext<'_>, registry: &mut ToolRegistr
         || !features.enabled(Feature::ShellTool)
         || !features.enabled(Feature::UnifiedExec)
         || matches!(
-            turn_context.model_info.shell_type,
+            turn_context.model_info().shell_type,
             ConfigShellToolType::Disabled
         )
     {
@@ -1051,7 +1053,7 @@ fn add_core_utility_tools(context: &CoreToolPlanContext<'_>, registry: &mut Tool
 
     if !turn_context.session_source.is_non_root_agent()
         && turn_context
-            .model_info
+            .model_info()
             .experimental_supported_tools
             .iter()
             .any(|tool| tool == "send_user_message_async")
@@ -1096,14 +1098,15 @@ fn add_core_utility_tools(context: &CoreToolPlanContext<'_>, registry: &mut Tool
         ));
     }
 
-    if environment_mode.has_environment() && turn_context.model_info.apply_patch_tool_type.is_some()
+    if environment_mode.has_environment()
+        && turn_context.model_info().apply_patch_tool_type.is_some()
     {
         let include_environment_id = matches!(environment_mode, ToolEnvironmentMode::Multiple);
         registry.add(ApplyPatchHandler::new(include_environment_id));
     }
 
     if turn_context
-        .model_info
+        .model_info()
         .experimental_supported_tools
         .iter()
         .any(|tool| tool == "test_sync_tool")
@@ -1115,11 +1118,11 @@ fn add_core_utility_tools(context: &CoreToolPlanContext<'_>, registry: &mut Tool
         let include_environment_id = matches!(environment_mode, ToolEnvironmentMode::Multiple);
         registry.add(ViewImageHandler::new(ViewImageToolOptions {
             can_request_original_image_detail: can_request_original_image_detail(
-                &turn_context.model_info,
+                turn_context.model_info(),
             ),
             unified_image_budget: unified_image_budget_enabled(
                 &turn_context.config.features,
-                &turn_context.model_info,
+                turn_context.model_info(),
             ),
             include_environment_id,
         }));
diff --git a/codex-rs/core/src/tools/spec_plan_tests.rs b/codex-rs/core/src/tools/spec_plan_tests.rs
index b5be3fbf08..b61f7e0f8b 100644
--- a/codex-rs/core/src/tools/spec_plan_tests.rs
+++ b/codex-rs/core/src/tools/spec_plan_tests.rs
@@ -1,3 +1,4 @@
+use crate::session::tests::update_turn_settings_for_test;
 use std::collections::BTreeMap;
 use std::sync::Arc;
 
@@ -532,7 +533,9 @@ async fn internal_guardian_sessions_respect_managed_shell_restrictions() {
             )
             .expect("managed shell restriction should be valid");
         }
-        Arc::make_mut(&mut turn.model_info).shell_type = shell_type;
+        update_turn_settings_for_test(&mut turn, |settings| {
+            Arc::make_mut(&mut settings.model_info).shell_type = shell_type;
+        });
         let turn = Arc::new(turn);
         let step_context = StepContext::for_test(Arc::clone(&turn));
 
@@ -850,7 +853,9 @@ async fn shell_family_registers_only_unified_exec_tools() {
     let plan = probe(|turn| {
         set_features(turn, &[Feature::ShellTool]);
         set_feature(turn, Feature::ShellZshFork, /*enabled*/ false);
-        Arc::make_mut(&mut turn.model_info).shell_type = ConfigShellToolType::UnifiedExec;
+        update_turn_settings_for_test(turn, |settings| {
+            Arc::make_mut(&mut settings.model_info).shell_type = ConfigShellToolType::UnifiedExec;
+        });
     })
     .await;
 
@@ -866,7 +871,10 @@ async fn login_shell_parameter_follows_selected_environment() {
             let plan = probe(|turn| {
                 set_feature(turn, Feature::ShellTool, /*enabled*/ true);
                 set_feature(turn, Feature::ShellZshFork, /*enabled*/ false);
-                Arc::make_mut(&mut turn.model_info).shell_type = ConfigShellToolType::UnifiedExec;
+                update_turn_settings_for_test(turn, |settings| {
+                    Arc::make_mut(&mut settings.model_info).shell_type =
+                        ConfigShellToolType::UnifiedExec;
+                });
                 update_config(turn, |config| {
                     config.permissions.allow_login_shell = !allow_login_shell;
                 });
@@ -922,7 +930,9 @@ async fn login_shell_parameter_is_available_when_any_environment_allows_it() {
 async fn disabling_shell_tools_disables_command_tools_for_all_environments() {
     let remote_environment = probe(|turn| {
         set_feature(turn, Feature::ShellTool, /*enabled*/ false);
-        Arc::make_mut(&mut turn.model_info).shell_type = ConfigShellToolType::UnifiedExec;
+        update_turn_settings_for_test(turn, |settings| {
+            Arc::make_mut(&mut settings.model_info).shell_type = ConfigShellToolType::UnifiedExec;
+        });
 
         let TurnEnvironmentState::Ready(environment) = turn
             .environments
@@ -946,7 +956,9 @@ async fn disabling_shell_tools_disables_command_tools_for_all_environments() {
 
     let multiple_local_environments = probe(|turn| {
         set_feature(turn, Feature::ShellTool, /*enabled*/ false);
-        Arc::make_mut(&mut turn.model_info).shell_type = ConfigShellToolType::UnifiedExec;
+        update_turn_settings_for_test(turn, |settings| {
+            Arc::make_mut(&mut settings.model_info).shell_type = ConfigShellToolType::UnifiedExec;
+        });
         duplicate_primary_environment(turn);
     })
     .await;
@@ -988,7 +1000,9 @@ async fn shell_zsh_fork_keeps_unified_exec_available() {
         set_features(turn, &[Feature::ShellTool]);
         set_feature(turn, Feature::ShellZshFork, /*enabled*/ true);
         set_feature(turn, Feature::UnifiedExecZshFork, /*enabled*/ false);
-        Arc::make_mut(&mut turn.model_info).shell_type = ConfigShellToolType::UnifiedExec;
+        update_turn_settings_for_test(turn, |settings| {
+            Arc::make_mut(&mut settings.model_info).shell_type = ConfigShellToolType::UnifiedExec;
+        });
     })
     .await;
 
@@ -1004,7 +1018,9 @@ async fn shell_zsh_fork_keeps_unified_exec_available() {
                 Feature::UnifiedExecZshFork,
             ],
         );
-        Arc::make_mut(&mut turn.model_info).shell_type = ConfigShellToolType::UnifiedExec;
+        update_turn_settings_for_test(turn, |settings| {
+            Arc::make_mut(&mut settings.model_info).shell_type = ConfigShellToolType::UnifiedExec;
+        });
     })
     .await;
 
@@ -1116,8 +1132,10 @@ async fn environment_count_controls_environment_backed_tools() {
         turn.environments.environments.clear();
         set_feature(turn, Feature::ShellTool, /*enabled*/ true);
         set_feature(turn, Feature::RequestPermissionsTool, /*enabled*/ true);
-        Arc::make_mut(&mut turn.model_info).apply_patch_tool_type =
-            Some(ApplyPatchToolType::Freeform);
+        update_turn_settings_for_test(turn, |settings| {
+            Arc::make_mut(&mut settings.model_info).apply_patch_tool_type =
+                Some(ApplyPatchToolType::Freeform);
+        });
     })
     .await;
     no_environment.assert_visible_lacks(&[
@@ -1139,8 +1157,10 @@ async fn environment_count_controls_environment_backed_tools() {
         duplicate_primary_environment(turn);
         set_feature(turn, Feature::ShellTool, /*enabled*/ true);
         set_feature(turn, Feature::RequestPermissionsTool, /*enabled*/ true);
-        Arc::make_mut(&mut turn.model_info).apply_patch_tool_type =
-            Some(ApplyPatchToolType::Freeform);
+        update_turn_settings_for_test(turn, |settings| {
+            Arc::make_mut(&mut settings.model_info).apply_patch_tool_type =
+                Some(ApplyPatchToolType::Freeform);
+        });
     })
     .await;
     multiple_environments.assert_visible_contains(&[
@@ -1165,7 +1185,10 @@ async fn environment_count_controls_environment_backed_tools() {
 #[tokio::test]
 async fn environment_tools_follow_the_step_context() {
     let (_session, mut turn) = make_session_and_context().await;
-    Arc::make_mut(&mut turn.model_info).apply_patch_tool_type = Some(ApplyPatchToolType::Freeform);
+    update_turn_settings_for_test(&mut turn, |settings| {
+        Arc::make_mut(&mut settings.model_info).apply_patch_tool_type =
+            Some(ApplyPatchToolType::Freeform);
+    });
 
     let environments = turn.environments.clone();
     turn.environments.environments.clear();
@@ -1295,7 +1318,9 @@ async fn mcp_and_tool_search_follow_direct_and_deferred_tool_exposure() {
 
     let missing_model_capability = probe_with(
         |turn| {
-            Arc::make_mut(&mut turn.model_info).supports_search_tool = false;
+            update_turn_settings_for_test(turn, |settings| {
+                Arc::make_mut(&mut settings.model_info).supports_search_tool = false;
+            });
         },
         searchable_mcp(),
     )
@@ -1304,7 +1329,9 @@ async fn mcp_and_tool_search_follow_direct_and_deferred_tool_exposure() {
 
     let missing_deferred_tools = probe(|turn| {
         set_feature(turn, Feature::Collab, /*enabled*/ false);
-        Arc::make_mut(&mut turn.model_info).supports_search_tool = true;
+        update_turn_settings_for_test(turn, |settings| {
+            Arc::make_mut(&mut settings.model_info).supports_search_tool = true;
+        });
     })
     .await;
     missing_deferred_tools.assert_visible_lacks(&["tool_search"]);
@@ -1316,7 +1343,9 @@ async fn mcp_and_tool_search_follow_direct_and_deferred_tool_exposure() {
 
     let bedrock_namespace_capability = probe_with(
         |turn| {
-            Arc::make_mut(&mut turn.model_info).supports_search_tool = true;
+            update_turn_settings_for_test(turn, |settings| {
+                Arc::make_mut(&mut settings.model_info).supports_search_tool = true;
+            });
             use_bedrock_provider(turn);
         },
         searchable_mcp(),
@@ -1326,7 +1355,9 @@ async fn mcp_and_tool_search_follow_direct_and_deferred_tool_exposure() {
 
     let enabled = probe_with(
         |turn| {
-            Arc::make_mut(&mut turn.model_info).supports_search_tool = true;
+            update_turn_settings_for_test(turn, |settings| {
+                Arc::make_mut(&mut settings.model_info).supports_search_tool = true;
+            });
         },
         searchable_mcp(),
     )
@@ -1340,7 +1371,9 @@ async fn mcp_and_tool_search_follow_direct_and_deferred_tool_exposure() {
     let reserved_namespace = probe_with(
         |turn| {
             set_feature(turn, Feature::CodeMode, /*enabled*/ true);
-            Arc::make_mut(&mut turn.model_info).supports_search_tool = true;
+            update_turn_settings_for_test(turn, |settings| {
+                Arc::make_mut(&mut settings.model_info).supports_search_tool = true;
+            });
         },
         ToolPlanInputs {
             tool_runtimes: vec![
@@ -1392,8 +1425,10 @@ async fn tool_namespaces_info_is_opt_in_and_tracks_mcp_exposure() {
                     config.tool_registry.turn_metadata_includes_tool_info = enabled;
                 });
                 set_feature(turn, Feature::CodeMode, /*enabled*/ true);
-                Arc::make_mut(&mut turn.model_info).supports_search_tool = true;
-                Arc::make_mut(&mut turn.model_info).use_responses_lite = true;
+                update_turn_settings_for_test(turn, |settings| {
+                    Arc::make_mut(&mut settings.model_info).supports_search_tool = true;
+                    Arc::make_mut(&mut settings.model_info).use_responses_lite = true;
+                });
                 metadata_state = Some(Arc::clone(&turn.turn_metadata_state));
             },
             ToolPlanInputs {
@@ -1467,7 +1502,9 @@ async fn strict_namespace_ownership_requires_tool_namespace_inventory_opt_in() {
             config.tool_registry.error_on_tool_collisions = true;
             config.tool_registry.turn_metadata_includes_tool_info = enabled;
         });
-        Arc::make_mut(&mut turn.model_info).use_responses_lite = true;
+        update_turn_settings_for_test(&mut turn, |settings| {
+            Arc::make_mut(&mut settings.model_info).use_responses_lite = true;
+        });
         let step_context = StepContext::for_test(Arc::new(turn));
         let mut registry = build_core_tool_registry(
             step_context.turn.as_ref(),
@@ -1522,7 +1559,10 @@ async fn unified_tool_runtimes_preserve_source_order_and_collision_priority() {
         |turn| {
             set_features(turn, &[Feature::ShellTool]);
             set_feature(turn, Feature::ShellZshFork, /*enabled*/ false);
-            Arc::make_mut(&mut turn.model_info).shell_type = ConfigShellToolType::UnifiedExec;
+            update_turn_settings_for_test(turn, |settings| {
+                Arc::make_mut(&mut settings.model_info).shell_type =
+                    ConfigShellToolType::UnifiedExec;
+            });
         },
         ToolPlanInputs {
             tool_runtimes: vec![mcp_runtime(
@@ -1718,7 +1758,9 @@ async fn strict_tool_collisions_reject_external_and_synthetic_duplicates() {
         if code_mode_enabled {
             set_feature(&mut turn, Feature::CodeMode, /*enabled*/ true);
         }
-        Arc::make_mut(&mut turn.model_info).supports_search_tool = search_enabled;
+        update_turn_settings_for_test(&mut turn, |settings| {
+            Arc::make_mut(&mut settings.model_info).supports_search_tool = search_enabled;
+        });
         let turn = Arc::new(turn);
         let step_context = StepContext::for_test(Arc::clone(&turn));
         let mut registry = build_core_tool_registry(
@@ -1876,8 +1918,10 @@ async fn code_mode_uses_the_first_normalized_tool_identity() {
                 if code_mode_only {
                     set_feature(turn, Feature::CodeModeOnly, /*enabled*/ true);
                 }
-                Arc::make_mut(&mut turn.model_info).supports_search_tool = true;
-                Arc::make_mut(&mut turn.model_info).use_responses_lite = true;
+                update_turn_settings_for_test(turn, |settings| {
+                    Arc::make_mut(&mut settings.model_info).supports_search_tool = true;
+                    Arc::make_mut(&mut settings.model_info).use_responses_lite = true;
+                });
                 metadata_state = Some(Arc::clone(&turn.turn_metadata_state));
             },
             ToolPlanInputs {
@@ -1960,7 +2004,9 @@ async fn code_mode_uses_the_first_normalized_tool_identity() {
 async fn deferred_extension_tools_are_discoverable_with_tool_search() {
     let plan = probe_with(
         |turn| {
-            Arc::make_mut(&mut turn.model_info).supports_search_tool = true;
+            update_turn_settings_for_test(turn, |settings| {
+                Arc::make_mut(&mut settings.model_info).supports_search_tool = true;
+            });
         },
         ToolPlanInputs {
             extension_tool_executors: vec![Arc::new(DeferredExtensionTool)],
@@ -1980,7 +2026,9 @@ async fn tool_search_cache_rebuilds_when_deferred_sources_change() {
     let cache = ToolSearchHandlerCache::default();
 
     let (_session, mut first_turn) = make_session_and_context().await;
-    Arc::make_mut(&mut first_turn.model_info).supports_search_tool = true;
+    update_turn_settings_for_test(&mut first_turn, |settings| {
+        Arc::make_mut(&mut settings.model_info).supports_search_tool = true;
+    });
     let first_turn = Arc::new(first_turn);
     let first_step_context = StepContext::for_test(Arc::clone(&first_turn));
     let mut first_registry = build_core_tool_registry(
@@ -2001,7 +2049,9 @@ async fn tool_search_cache_rebuilds_when_deferred_sources_change() {
     let first_plan = ToolPlanProbe::from_router(first_router);
 
     let (_session, mut second_turn) = make_session_and_context().await;
-    Arc::make_mut(&mut second_turn.model_info).supports_search_tool = true;
+    update_turn_settings_for_test(&mut second_turn, |settings| {
+        Arc::make_mut(&mut settings.model_info).supports_search_tool = true;
+    });
     let second_turn = Arc::new(second_turn);
     let second_step_context = StepContext::for_test(Arc::clone(&second_turn));
     let mut second_registry = build_core_tool_registry(
@@ -2048,7 +2098,9 @@ async fn tool_search_cache_rebuilds_when_deferred_world_state_changes() {
 
     for world_state_enabled in [false, true, false] {
         let (_session, mut turn) = make_session_and_context().await;
-        Arc::make_mut(&mut turn.model_info).supports_search_tool = true;
+        update_turn_settings_for_test(&mut turn, |settings| {
+            Arc::make_mut(&mut settings.model_info).supports_search_tool = true;
+        });
         set_feature(
             &mut turn,
             Feature::DeferredToolWorldState,
@@ -2161,7 +2213,9 @@ async fn request_plugin_install_requires_all_discovery_features() {
 async fn request_plugin_install_stays_visible_without_tool_search() {
     let plan = probe_with(
         |turn| {
-            Arc::make_mut(&mut turn.model_info).supports_search_tool = false;
+            update_turn_settings_for_test(turn, |settings| {
+                Arc::make_mut(&mut settings.model_info).supports_search_tool = false;
+            });
             set_features(
                 turn,
                 &[Feature::ToolSuggest, Feature::Apps, Feature::Plugins],
@@ -2297,7 +2351,9 @@ async fn code_mode_only_exposes_configured_dynamic_namespace_directly() {
     let plan = probe_with(
         |turn| {
             set_features(turn, &[Feature::CodeMode, Feature::CodeModeOnly]);
-            Arc::make_mut(&mut turn.model_info).supports_search_tool = true;
+            update_turn_settings_for_test(turn, |settings| {
+                Arc::make_mut(&mut settings.model_info).supports_search_tool = true;
+            });
             update_config(turn, |config| {
                 config.code_mode.direct_only_tool_namespaces = vec!["direct_only".to_string()];
             });
@@ -2361,7 +2417,9 @@ async fn excluded_deferred_namespaces_do_not_enable_nested_tool_guidance() {
         |turn| {
             set_features(turn, &[Feature::CodeMode, Feature::CodeModeOnly]);
             set_feature(turn, Feature::Collab, /*enabled*/ false);
-            Arc::make_mut(&mut turn.model_info).supports_search_tool = true;
+            update_turn_settings_for_test(turn, |settings| {
+                Arc::make_mut(&mut settings.model_info).supports_search_tool = true;
+            });
             update_config(turn, |config| {
                 config.code_mode.excluded_tool_namespaces = vec!["excluded".to_string()];
             });
@@ -2615,7 +2673,9 @@ async fn multi_agent_v2_can_disable_wait_agent() {
 async fn tool_mode_selector_overrides_feature_flags() {
     let direct = probe(|turn| {
         set_features(turn, &[Feature::CodeMode, Feature::CodeModeOnly]);
-        Arc::make_mut(&mut turn.model_info).tool_mode = Some(ToolMode::Direct);
+        update_turn_settings_for_test(turn, |settings| {
+            Arc::make_mut(&mut settings.model_info).tool_mode = Some(ToolMode::Direct);
+        });
     })
     .await;
     direct.assert_visible_lacks(&[
@@ -2627,7 +2687,9 @@ async fn tool_mode_selector_overrides_feature_flags() {
 #[tokio::test]
 async fn v1_multi_agent_tools_defer_when_tool_search_available() {
     let plan = probe(|turn| {
-        Arc::make_mut(&mut turn.model_info).supports_search_tool = true;
+        update_turn_settings_for_test(turn, |settings| {
+            Arc::make_mut(&mut settings.model_info).supports_search_tool = true;
+        });
         set_feature(turn, Feature::Collab, /*enabled*/ true);
         set_feature(turn, Feature::MultiAgentV2, /*enabled*/ false);
     })
@@ -2770,8 +2832,11 @@ async fn multi_agent_v2_bedrock_workers_only_delegate_when_model_supports_v2() {
                 config.multi_agent_v2.tool_namespace = Some("agents".to_string());
             });
             use_bedrock_provider(turn);
-            Arc::make_mut(&mut turn.model_info).slug = model.to_string();
-            Arc::make_mut(&mut turn.model_info).multi_agent_version = model_multi_agent_version;
+            update_turn_settings_for_test(turn, |settings| {
+                Arc::make_mut(&mut settings.model_info).slug = model.to_string();
+                Arc::make_mut(&mut settings.model_info).multi_agent_version =
+                    model_multi_agent_version;
+            });
             turn.session_source = SessionSource::SubAgent(SubAgentSource::ThreadSpawn {
                 parent_thread_id: ThreadId::new(),
                 depth: 1,
@@ -2886,7 +2951,10 @@ async fn hosted_web_search_and_standalone_image_generation_follow_runtime_gates(
     let image_generation = probe_with(
         |turn| {
             use_chatgpt_auth(turn);
-            Arc::make_mut(&mut turn.model_info).input_modalities = vec![InputModality::Image];
+            update_turn_settings_for_test(turn, |settings| {
+                Arc::make_mut(&mut settings.model_info).input_modalities =
+                    vec![InputModality::Image];
+            });
         },
         ToolPlanInputs {
             extension_tool_executors: vec![image_generation_tool.clone()],
@@ -2900,7 +2968,10 @@ async fn hosted_web_search_and_standalone_image_generation_follow_runtime_gates(
         |turn| {
             use_chatgpt_auth(turn);
             set_feature(turn, Feature::ImageGeneration, /*enabled*/ false);
-            Arc::make_mut(&mut turn.model_info).input_modalities = vec![InputModality::Image];
+            update_turn_settings_for_test(turn, |settings| {
+                Arc::make_mut(&mut settings.model_info).input_modalities =
+                    vec![InputModality::Image];
+            });
         },
         ToolPlanInputs {
             extension_tool_executors: vec![image_generation_tool.clone()],
@@ -2913,7 +2984,9 @@ async fn hosted_web_search_and_standalone_image_generation_follow_runtime_gates(
     let text_only_model = probe_with(
         |turn| {
             use_chatgpt_auth(turn);
-            Arc::make_mut(&mut turn.model_info).input_modalities = vec![];
+            update_turn_settings_for_test(turn, |settings| {
+                Arc::make_mut(&mut settings.model_info).input_modalities = vec![];
+            });
         },
         ToolPlanInputs {
             extension_tool_executors: vec![image_generation_tool.clone()],
@@ -2926,7 +2999,10 @@ async fn hosted_web_search_and_standalone_image_generation_follow_runtime_gates(
     let unsupported_provider = probe_with(
         |turn| {
             use_bedrock_provider(turn);
-            Arc::make_mut(&mut turn.model_info).input_modalities = vec![InputModality::Image];
+            update_turn_settings_for_test(turn, |settings| {
+                Arc::make_mut(&mut settings.model_info).input_modalities =
+                    vec![InputModality::Image];
+            });
         },
         ToolPlanInputs {
             extension_tool_executors: vec![image_generation_tool],
@@ -2938,7 +3014,10 @@ async fn hosted_web_search_and_standalone_image_generation_follow_runtime_gates(
 
     let live_web_search = probe(|turn| {
         set_web_search_mode(turn, WebSearchMode::Live);
-        Arc::make_mut(&mut turn.model_info).web_search_tool_type = WebSearchToolType::TextAndImage;
+        update_turn_settings_for_test(turn, |settings| {
+            Arc::make_mut(&mut settings.model_info).web_search_tool_type =
+                WebSearchToolType::TextAndImage;
+        });
     })
     .await;
     assert_eq!(
@@ -2957,7 +3036,9 @@ async fn hosted_web_search_and_standalone_image_generation_follow_runtime_gates(
         use_chatgpt_auth(turn);
         set_features(turn, &[Feature::CodeModeOnly, Feature::MultiAgentV2]);
         set_web_search_mode(turn, WebSearchMode::Live);
-        Arc::make_mut(&mut turn.model_info).input_modalities = vec![InputModality::Image];
+        update_turn_settings_for_test(turn, |settings| {
+            Arc::make_mut(&mut settings.model_info).input_modalities = vec![InputModality::Image];
+        });
     })
     .await;
     assert_eq!(
@@ -3034,7 +3115,9 @@ async fn hosted_web_search_and_standalone_image_generation_follow_runtime_gates(
 
     let bedrock_cached_web_search = probe(|turn| {
         use_bedrock_provider(turn);
-        Arc::make_mut(&mut turn.model_info).web_search_tool_type = WebSearchToolType::Text;
+        update_turn_settings_for_test(turn, |settings| {
+            Arc::make_mut(&mut settings.model_info).web_search_tool_type = WebSearchToolType::Text;
+        });
     })
     .await;
     assert_eq!(
@@ -3053,7 +3136,9 @@ async fn hosted_web_search_and_standalone_image_generation_follow_runtime_gates(
         set_feature(turn, Feature::StandaloneWebSearch, /*enabled*/ true);
         set_web_search_mode(turn, WebSearchMode::Cached);
         use_bedrock_provider(turn);
-        Arc::make_mut(&mut turn.model_info).web_search_tool_type = WebSearchToolType::Text;
+        update_turn_settings_for_test(turn, |settings| {
+            Arc::make_mut(&mut settings.model_info).web_search_tool_type = WebSearchToolType::Text;
+        });
     })
     .await;
     bedrock_with_standalone_web_search.assert_visible_contains(&["web_search"]);
diff --git a/codex-rs/core/src/unified_exec/mod_tests.rs b/codex-rs/core/src/unified_exec/mod_tests.rs
index 3ba46c2b03..b4f352d015 100644
--- a/codex-rs/core/src/unified_exec/mod_tests.rs
+++ b/codex-rs/core/src/unified_exec/mod_tests.rs
@@ -193,7 +193,7 @@ async fn exec_command_with_tty(
         chunk_id: generate_chunk_id(),
         wall_time,
         raw_output: collected,
-        truncation_policy: turn.model_info.truncation_policy.into(),
+        truncation_policy: turn.model_info().truncation_policy.into(),
         max_output_tokens: None,
         process_id: response_process_id,
         exit_code,
diff --git a/codex-rs/core/src/unified_exec/process_manager.rs b/codex-rs/core/src/unified_exec/process_manager.rs
index 181551409d..ed0da71297 100644
--- a/codex-rs/core/src/unified_exec/process_manager.rs
+++ b/codex-rs/core/src/unified_exec/process_manager.rs
@@ -741,7 +741,7 @@ impl UnifiedExecProcessManager {
             truncation_policy: context
                 .step_context
                 .turn
-                .model_info
+                .model_info()
                 .truncation_policy
                 .into(),
             max_output_tokens: request.max_output_tokens,
diff --git a/codex-rs/core/src/user_shell_command.rs b/codex-rs/core/src/user_shell_command.rs
index e64cf64cdf..02f52e060d 100644
--- a/codex-rs/core/src/user_shell_command.rs
+++ b/codex-rs/core/src/user_shell_command.rs
@@ -13,7 +13,7 @@ fn user_shell_command_fragment(
 ) -> UserShellCommand {
     let output = format_exec_output_str(
         exec_output,
-        turn_context.model_info.truncation_policy.into(),
+        turn_context.model_info().truncation_policy.into(),
     );
     UserShellCommand::new(command, exec_output.exit_code, exec_output.duration, output)
 }
diff --git a/codex-rs/core/tests/suite/compact.rs b/codex-rs/core/tests/suite/compact.rs
index d94239d4ac..40c74d0a04 100644
--- a/codex-rs/core/tests/suite/compact.rs
+++ b/codex-rs/core/tests/suite/compact.rs
@@ -14,10 +14,13 @@ use codex_models_manager::bundled_models_response;
 use codex_protocol::config_types::AutoCompactTokenLimitScope;
 use codex_protocol::config_types::CollaborationMode;
 use codex_protocol::config_types::ModeKind;
+use codex_protocol::config_types::ReasoningSummary;
+use codex_protocol::config_types::ServiceTier;
 use codex_protocol::config_types::Settings;
 use codex_protocol::items::TurnItem;
 use codex_protocol::models::PermissionProfile;
 use codex_protocol::openai_models::ModelInfo;
+use codex_protocol::openai_models::ModelServiceTier;
 use codex_protocol::openai_models::ModelsResponse;
 use codex_protocol::protocol::AskForApproval;
 use codex_protocol::protocol::EventMsg;
@@ -2280,6 +2283,97 @@ async fn pre_sampling_compact_runs_when_comp_hash_changes() {
     );
 }
 
+#[tokio::test(flavor = "multi_thread", worker_threads = 2)]
+async fn previous_model_compaction_resolves_selected_settings() -> Result<()> {
+    skip_if_no_network!(Ok(()));
+    let server = start_mock_server().await;
+    let request_log = mount_sse_sequence(
+        &server,
+        vec![
+            sse(vec![
+                ev_assistant_message("m1", "before switch"),
+                ev_completed("r1"),
+            ]),
+            sse(vec![
+                ev_assistant_message("m2", "COMPACTION_SUMMARY"),
+                ev_completed("r2"),
+            ]),
+            responses::sse_completed("r3"),
+        ],
+    )
+    .await;
+    let model_provider = non_openai_model_provider(&server);
+    let test = test_codex()
+        .with_model_info_override("gpt-5.4", |model| {
+            model.comp_hash = Some("hash-a".to_string());
+            model.default_reasoning_summary = ReasoningSummary::Detailed;
+            model.service_tiers = vec![ModelServiceTier {
+                id: ServiceTier::Fast.request_value().to_string(),
+                name: "Fast".to_string(),
+                description: "Priority processing".to_string(),
+            }];
+        })
+        .with_model_info_override("gpt-5.2", |model| {
+            model.comp_hash = Some("hash-b".to_string());
+            model.default_reasoning_summary = ReasoningSummary::Auto;
+            model.service_tiers.clear();
+        })
+        .with_model("gpt-5.4")
+        .with_config(move |config| {
+            config.model_provider = model_provider;
+            config.model_reasoning_summary = None;
+            config.service_tier = Some(ServiceTier::Fast.request_value().to_string());
+            config
+                .features
+                .enable(Feature::FastMode)
+                .expect("enable FastMode");
+            set_test_compact_prompt(config);
+        })
+        .build_with_auto_env(&server)
+        .await?;
+    test.submit_text_turn("before switch").await?;
+    test.codex
+        .start_or_steer_turn(
+            TurnInputRequest::user_input(vec![UserInput::Text {
+                text: "after switch".to_string(),
+                text_elements: Vec::new(),
+            }])
+            .with_thread_settings(ThreadSettingsOverrides {
+                model: Some("gpt-5.2".to_string()),
+                ..Default::default()
+            }),
+        )
+        .await?;
+    wait_for_event(&test.codex, |event| {
+        matches!(event, EventMsg::TurnComplete(_))
+    })
+    .await;
+
+    // The retained priority selection is filtered out for B, restored for
+    // compaction on A, and still omitted from the following B request.
+    let actual = request_log
+        .requests()
+        .iter()
+        .map(|request| {
+            let body = request.body_json();
+            json!([
+                body["model"],
+                body["reasoning"]["summary"],
+                body["service_tier"]
+            ])
+        })
+        .collect::<Vec<_>>();
+    assert_eq!(
+        actual,
+        vec![
+            json!(["gpt-5.4", "detailed", "priority"]),
+            json!(["gpt-5.4", "detailed", "priority"]),
+            json!(["gpt-5.2", "auto", null]),
+        ]
+    );
+    Ok(())
+}
+
 #[tokio::test(flavor = "multi_thread", worker_threads = 2)]
 async fn pre_sampling_compact_falls_back_from_retired_previous_model_after_rename() {
     skip_if_no_network!();
diff --git a/codex-rs/core/tests/suite/mod.rs b/codex-rs/core/tests/suite/mod.rs
index ba0f21285b..c60d695a96 100644
--- a/codex-rs/core/tests/suite/mod.rs
+++ b/codex-rs/core/tests/suite/mod.rs
@@ -153,6 +153,7 @@ mod skills;
 mod skills_extension;
 mod spawn_agent_description;
 mod sqlite_state;
+mod step_settings_snapshots;
 mod stream_error_allows_next_turn;
 mod stream_no_completed;
 mod subagent_notifications;
diff --git a/codex-rs/core/tests/suite/review.rs b/codex-rs/core/tests/suite/review.rs
index f095d56e55..d926e9dc2f 100644
--- a/codex-rs/core/tests/suite/review.rs
+++ b/codex-rs/core/tests/suite/review.rs
@@ -10,7 +10,12 @@ use codex_history::RolloutItem;
 use codex_history::RolloutLine;
 use codex_login::CodexAuth;
 use codex_protocol::config_types::ApprovalsReviewer;
+use codex_protocol::config_types::CollaborationMode;
+use codex_protocol::config_types::ModeKind;
+use codex_protocol::config_types::Personality;
+use codex_protocol::config_types::ReasoningSummary;
 use codex_protocol::config_types::ServiceTier;
+use codex_protocol::config_types::Settings;
 use codex_protocol::items::TurnItem;
 use codex_protocol::models::ContentItem;
 use codex_protocol::models::PermissionProfile;
@@ -627,6 +632,10 @@ async fn review_uses_updated_turn_permissions_and_approval_policy() {
             config.review_model = Some("gpt-5.4".to_string());
             config.model_context_window = Some(128_000);
             config.service_tier = Some(ServiceTier::Fast.request_value().to_string());
+            config
+                .features
+                .enable(Feature::FastMode)
+                .expect("enable FastMode");
             config
                 .features
                 .enable(Feature::TokenBudget)
@@ -671,13 +680,22 @@ async fn review_uses_updated_turn_permissions_and_approval_policy() {
             approval_policy: Some(AskForApproval::Never),
             approvals_reviewer: Some(ApprovalsReviewer::User),
             permission_profile: Some(PermissionProfile::Disabled),
-            effort: Some(Some(ReasoningEffort::XHigh)),
+            personality: Some(Personality::Friendly),
+            collaboration_mode: Some(CollaborationMode {
+                mode: ModeKind::Plan,
+                settings: Settings {
+                    model: "gpt-5.2".to_string(),
+                    reasoning_effort: Some(ReasoningEffort::XHigh),
+                    developer_instructions: Some("Parent planning instructions".to_string()),
+                },
+            }),
             ..Default::default()
         },
     )
     .await
     .expect("updated thread permissions should be accepted");
 
+    let stored_settings = codex.thread_settings_snapshot().await;
     codex
         .submit(Op::Review {
             review_request: ReviewRequest {
@@ -691,6 +709,7 @@ async fn review_uses_updated_turn_permissions_and_approval_policy() {
         .expect("review should start");
     wait_for_event(&codex, |event| matches!(event, EventMsg::TurnComplete(_))).await;
 
+    assert_eq!(codex.thread_settings_snapshot().await, stored_settings);
     let request = request_log.single_request();
     assert_eq!(request.body_json()["reasoning"]["effort"], "medium");
     assert_eq!(
@@ -751,23 +770,166 @@ async fn review_uses_updated_turn_permissions_and_approval_policy() {
         })
         .expect("review rollout should contain session metadata");
     assert_eq!(review_session_cwd, updated_cwd.as_path());
-    let review_approvals_reviewer = review_rollout
+    let review_context = review_rollout
         .lines()
         .filter_map(|line| {
             let rollout_line: RolloutLine =
                 serde_json::from_str(line).expect("review rollout line should be valid");
             match rollout_line.item {
-                RolloutItem::TurnContext(turn_context) => turn_context.approvals_reviewer,
+                RolloutItem::TurnContext(turn_context) => Some(turn_context),
                 _ => None,
             }
         })
-        .next_back();
-    assert_eq!(review_approvals_reviewer, Some(ApprovalsReviewer::User));
+        .next_back()
+        .expect("review rollout should contain turn context");
+    assert_eq!(
+        review_context.approvals_reviewer,
+        Some(ApprovalsReviewer::User)
+    );
+    assert_eq!(review_context.personality, Some(Personality::Friendly));
+    // The review delegate still starts in its own default mode, not the parent's Plan mode.
+    assert_eq!(
+        review_context.collaboration_mode,
+        Some(CollaborationMode {
+            mode: ModeKind::Default,
+            settings: Settings {
+                model: "gpt-5.4".to_string(),
+                reasoning_effort: Some(ReasoningEffort::Medium),
+                developer_instructions: None,
+            },
+        })
+    );
 
     let _codex_home_guard = codex_home;
     server.verify().await;
 }
 
+#[tokio::test(flavor = "multi_thread", worker_threads = 2)]
+async fn review_omits_retained_tier_when_fast_mode_disabled() -> anyhow::Result<()> {
+    skip_if_no_network!(Ok(()));
+    let (server, request_log) =
+        start_responses_server_with_sse(completed_sse(), /*expected_requests*/ 1).await;
+    let test = test_codex()
+        .with_model_info_override("gpt-5.4", |model| {
+            model.service_tiers = vec![ModelServiceTier {
+                id: ServiceTier::Flex.request_value().to_string(),
+                name: "Flex".to_string(),
+                description: "Flexible processing".to_string(),
+            }];
+        })
+        .with_config(|config| {
+            config
+                .features
+                .disable(Feature::FastMode)
+                .expect("disable FastMode");
+        })
+        .build_with_auto_env(&server)
+        .await?;
+    core_test_support::submit_thread_settings(
+        &test.codex,
+        ThreadSettingsOverrides {
+            service_tier: Some(Some(ServiceTier::Flex.request_value().to_string())),
+            ..Default::default()
+        },
+    )
+    .await?;
+    test.codex
+        .submit(Op::Review {
+            review_request: ReviewRequest {
+                target: ReviewTarget::Custom {
+                    instructions: "review the changes".to_string(),
+                },
+                user_facing_hint: None,
+            },
+        })
+        .await?;
+    wait_for_event(&test.codex, |event| {
+        matches!(event, EventMsg::TurnComplete(_))
+    })
+    .await;
+
+    assert_eq!(
+        test.codex
+            .thread_settings_snapshot()
+            .await
+            .service_tier
+            .as_deref(),
+        Some("flex")
+    );
+    assert_eq!(
+        request_log.single_request().body_json().get("service_tier"),
+        None
+    );
+    Ok(())
+}
+
+#[tokio::test(flavor = "multi_thread", worker_threads = 2)]
+async fn review_resolves_inherited_summary_preferences() -> anyhow::Result<()> {
+    skip_if_no_network!(Ok(()));
+    let (server, request_log) =
+        start_responses_server_with_sse(completed_sse(), /*expected_requests*/ 2).await;
+    let test = test_codex()
+        .with_model_info_override("gpt-5.2", |model| {
+            model.default_reasoning_summary = ReasoningSummary::Auto;
+        })
+        .with_model_info_override("gpt-5.4", |model| {
+            model.default_reasoning_summary = ReasoningSummary::Detailed;
+        })
+        .with_model("gpt-5.2")
+        .with_config(|config| {
+            config.review_model = Some("gpt-5.4".to_string());
+            config.model_reasoning_summary = None;
+        })
+        .build_with_auto_env(&server)
+        .await?;
+
+    // First follow the review model's default, then use a preference updated on the thread.
+    for summary in [None, Some(ReasoningSummary::Concise)] {
+        if let Some(summary) = summary {
+            core_test_support::submit_thread_settings(
+                &test.codex,
+                ThreadSettingsOverrides {
+                    summary: Some(summary),
+                    ..Default::default()
+                },
+            )
+            .await?;
+        }
+        let stored_settings = test.codex.thread_settings_snapshot().await;
+        test.codex
+            .submit(Op::Review {
+                review_request: ReviewRequest {
+                    target: ReviewTarget::Custom {
+                        instructions: "review the changes".to_string(),
+                    },
+                    user_facing_hint: None,
+                },
+            })
+            .await?;
+        wait_for_event(&test.codex, |event| {
+            matches!(event, EventMsg::TurnComplete(_))
+        })
+        .await;
+        assert_eq!(test.codex.thread_settings_snapshot().await, stored_settings);
+    }
+    let actual = request_log
+        .requests()
+        .iter()
+        .map(|request| {
+            let body = request.body_json();
+            serde_json::json!([body["model"], body["reasoning"]["summary"]])
+        })
+        .collect::<Vec<_>>();
+    assert_eq!(
+        actual,
+        vec![
+            serde_json::json!(["gpt-5.4", "detailed"]),
+            serde_json::json!(["gpt-5.4", "concise"]),
+        ]
+    );
+    Ok(())
+}
+
 /// Ensure that when a custom `review_model` is set in the config, the review
 /// request uses that model (and not the main chat model).
 #[tokio::test(flavor = "multi_thread", worker_threads = 2)]
diff --git a/codex-rs/core/tests/suite/step_settings_snapshots.rs b/codex-rs/core/tests/suite/step_settings_snapshots.rs
new file mode 100644
index 0000000000..a31f8dfc3f
--- /dev/null
+++ b/codex-rs/core/tests/suite/step_settings_snapshots.rs
@@ -0,0 +1,171 @@
+use anyhow::Result;
+use codex_core::TurnInputRequest;
+use codex_features::Feature;
+use codex_models_manager::bundled_models_response;
+use codex_protocol::config_types::ReasoningSummary;
+use codex_protocol::config_types::ServiceTier;
+use codex_protocol::openai_models::ModelsResponse;
+use codex_protocol::openai_models::ReasoningEffort;
+use codex_protocol::protocol::EventMsg;
+use codex_protocol::protocol::Op;
+use codex_protocol::protocol::ThreadSettingsOverrides;
+use codex_protocol::request_user_input::RequestUserInputAnswer;
+use codex_protocol::request_user_input::RequestUserInputResponse;
+use codex_protocol::user_input::UserInput;
+use core_test_support::responses;
+use core_test_support::skip_if_no_network;
+use core_test_support::submit_thread_settings;
+use core_test_support::test_codex::test_codex;
+use core_test_support::wait_for_event;
+use core_test_support::wait_for_event_match;
+use pretty_assertions::assert_eq;
+use serde_json::json;
+use std::collections::HashMap;
+
+#[tokio::test(flavor = "multi_thread", worker_threads = 2)]
+async fn ordinary_settings_updates_keep_the_running_turn_snapshot() -> Result<()> {
+    skip_if_no_network!(Ok(()));
+    let server = responses::start_mock_server().await;
+    let response_mock = responses::mount_sse_sequence(
+        &server,
+        vec![
+            responses::sse(vec![
+                responses::ev_response_created("response-1"),
+                responses::ev_function_call(
+                    "pause",
+                    "request_user_input",
+                    &json!({ "questions": [{
+                        "id": "continue",
+                        "header": "Continue",
+                        "question": "Continue after the settings update?",
+                        "options": [
+                            { "label": "Yes", "description": "Continue the turn." },
+                            { "label": "No", "description": "Stop the turn." }
+                        ]
+                    }] })
+                    .to_string(),
+                ),
+                responses::ev_completed("response-1"),
+            ]),
+            responses::sse_completed("response-2"),
+            responses::sse_completed("response-3"),
+        ],
+    )
+    .await;
+    let test = test_codex()
+        .with_model("snapshot-model-a")
+        .with_config(|config| {
+            // This regression exercises ordinary turn construction without
+            // enabling the diagnostic active-settings path.
+            config
+                .features
+                .enable(Feature::DefaultModeRequestUserInput)
+                .unwrap();
+            config.features.enable(Feature::FastMode).unwrap();
+            let template = bundled_models_response()
+                .unwrap()
+                .models
+                .into_iter()
+                .find(|model| model.slug == "gpt-5.4")
+                .unwrap();
+            config.model_catalog = Some(ModelsResponse {
+                models: ["snapshot-model-a", "snapshot-model-b"]
+                    .into_iter()
+                    .map(|slug| {
+                        let mut model = template.clone();
+                        model.slug = slug.to_string();
+                        model.default_reasoning_summary = ReasoningSummary::Concise;
+                        model
+                    })
+                    .collect(),
+            });
+            config.model_reasoning_effort = Some(ReasoningEffort::Low);
+            config.model_reasoning_summary = None;
+            config.service_tier = None;
+        })
+        .build_with_auto_env(&server)
+        .await?;
+    test.codex
+        .start_or_steer_turn(TurnInputRequest::user_input(vec![UserInput::Text {
+            text: "pause before continuing".into(),
+            text_elements: Vec::new(),
+        }]))
+        .await?;
+    let paused = wait_for_event_match(&test.codex, |event| match event {
+        EventMsg::RequestUserInput(request) => Some(request.clone()),
+        _ => None,
+    })
+    .await;
+
+    let mut expected = test.codex.thread_settings_snapshot().await;
+    submit_thread_settings(
+        &test.codex,
+        ThreadSettingsOverrides {
+            model: Some("snapshot-model-b".to_string()),
+            effort: Some(Some(ReasoningEffort::High)),
+            summary: Some(ReasoningSummary::Detailed),
+            service_tier: Some(Some(ServiceTier::Fast.request_value().to_string())),
+            ..Default::default()
+        },
+    )
+    .await?;
+    expected.model = "snapshot-model-b".to_string();
+    expected.reasoning_effort = Some(ReasoningEffort::High);
+    expected.reasoning_summary = Some(ReasoningSummary::Detailed);
+    expected.service_tier = Some(ServiceTier::Fast.request_value().to_string());
+    expected.collaboration_mode = expected.collaboration_mode.with_updates(
+        Some(expected.model.clone()),
+        Some(expected.reasoning_effort.clone()),
+        /*developer_instructions*/ None,
+    );
+    assert_eq!(test.codex.thread_settings_snapshot().await, expected);
+    test.codex
+        .submit(Op::UserInputAnswer {
+            id: paused.turn_id.clone(),
+            response: RequestUserInputResponse {
+                answers: HashMap::from([(
+                    "continue".to_string(),
+                    RequestUserInputAnswer {
+                        answers: vec!["Yes".to_string()],
+                    },
+                )]),
+            },
+        })
+        .await?;
+    wait_for_event(&test.codex, |event| {
+        matches!(event, EventMsg::TurnComplete(_))
+    })
+    .await;
+    test.submit_text_turn("start the next turn").await?;
+
+    let requests = response_mock.requests();
+    let actual = requests
+        .iter()
+        .map(|request| {
+            let body = request.body_json();
+            json!({
+                "model": body["model"],
+                "reasoning": body["reasoning"],
+                "service_tier": body.get("service_tier"),
+            })
+        })
+        .collect::<Vec<_>>();
+    let original = json!({
+        "model": "snapshot-model-a",
+        "reasoning": { "effort": "low", "summary": "concise" },
+        "service_tier": null,
+    });
+    assert_eq!(
+        actual,
+        vec![
+            original.clone(),
+            original,
+            json!({
+                "model": "snapshot-model-b",
+                "reasoning": { "effort": "high", "summary": "detailed" },
+                "service_tier": "priority",
+            })
+        ]
+    );
+    Ok(())
+}