diff --git a/codex-rs/app-server/tests/common/models_cache.rs b/codex-rs/app-server/tests/common/models_cache.rs
index e00e269222..0b14bc0035 100644
--- a/codex-rs/app-server/tests/common/models_cache.rs
+++ b/codex-rs/app-server/tests/common/models_cache.rs
@@ -67,6 +67,7 @@ fn preset_to_info(preset: &ModelPreset, priority: i32) -> ModelInfo {
         supports_search_tool: false,
         supports_experimental_context: false,
         use_responses_lite: false,
+        supports_reasoning_effort_updates: false,
         guardian: None,
         node_repl_auto_review_required: false,
         node_repl_disabled: false,
diff --git a/codex-rs/codex-api/tests/models_integration.rs b/codex-rs/codex-api/tests/models_integration.rs
index b02958ffa8..2227437618 100644
--- a/codex-rs/codex-api/tests/models_integration.rs
+++ b/codex-rs/codex-api/tests/models_integration.rs
@@ -155,6 +155,7 @@ async fn models_client_hits_models_endpoint() {
             supports_search_tool: false,
             supports_experimental_context: false,
             use_responses_lite: false,
+            supports_reasoning_effort_updates: true,
             guardian: None,
             node_repl_auto_review_required: true,
             node_repl_disabled: true,
diff --git a/codex-rs/core/src/client.rs b/codex-rs/core/src/client.rs
index c3724aee0a..637ce95e7c 100644
--- a/codex-rs/core/src/client.rs
+++ b/codex-rs/core/src/client.rs
@@ -528,8 +528,10 @@ impl ModelClient {
         }
     }
 
-    pub(crate) fn reasoning_effort_override_enabled(&self) -> bool {
+    pub(crate) fn reasoning_effort_override_enabled(&self, model_info: &ModelInfo) -> bool {
         self.state.reasoning_effort_override_enabled
+            && self.state.provider.info().is_openai()
+            && model_info.supports_reasoning_effort_updates
     }
 
     pub(crate) fn with_restored_history(mut self, restored_history: bool) -> Self {
@@ -867,8 +869,8 @@ impl ModelClient {
         responses_metadata: &CodexResponsesMetadata,
     ) -> Result<ResponsesApiRequest> {
         let mut input = prompt.get_formatted_input_for_request(model_info);
-        if !self.state.reasoning_effort_override_enabled {
-            // Disabling overrides must also recover threads with saved updates.
+        if !self.reasoning_effort_override_enabled(model_info) {
+            // Unsupported models and disabled overrides must also accept saved history.
             // Filter only the request copy; persisted history remains unchanged.
             input.retain(|item| !matches!(item, ResponseItem::ConfigurationUpdate { .. }));
         }
diff --git a/codex-rs/core/src/session/reasoning_effort.rs b/codex-rs/core/src/session/reasoning_effort.rs
index 3ff9e4049f..19e00db3c7 100644
--- a/codex-rs/core/src/session/reasoning_effort.rs
+++ b/codex-rs/core/src/session/reasoning_effort.rs
@@ -4,6 +4,7 @@
 //! baseline while it is retained.
 //! Successful compaction retires the overrides and allows a fresh request baseline.
 //! Synchronous Guardian reviewers always use their selected request-level effort.
+//! Unsupported models use selected request effort without rewriting saved updates.
 
 use super::session::Session;
 use super::step_context::StepContext;
@@ -26,7 +27,7 @@ impl Session {
     /// Establishes the selected effort in surviving history, independent of replayed settings.
     pub(crate) async fn record_reasoning_effort_override(&self, step_context: &StepContext) {
         let settings = &step_context.settings;
-        let Some(effort) = self.effort_for_configuration_update(settings).await else {
+        let Some(effort) = self.effort_for_configuration_update(settings) else {
             return;
         };
         let should_skip = {
@@ -99,8 +100,11 @@ impl Session {
         if !self
             .services
             .model_client
-            .reasoning_effort_override_enabled()
+            .reasoning_effort_override_enabled(&settings.model_info)
         {
+            if usage == RequestEffortUsage::Sampling {
+                self.state.lock().await.reasoning_effort_pin = ReasoningEffortPin::Unset;
+            }
             return selected_effort;
         }
         if usage == RequestEffortUsage::Compaction
@@ -113,7 +117,7 @@ impl Session {
         {
             return Some(pinned);
         }
-        let effort = self.effort_for_configuration_update(settings).await;
+        let effort = self.effort_for_configuration_update(settings);
         let mut state = self.state.lock().await;
         let Some(effort) = effort else {
             if usage == RequestEffortUsage::Sampling {
@@ -130,16 +134,14 @@ impl Session {
         })
     }
 
-    async fn effort_for_configuration_update(
+    fn effort_for_configuration_update(
         &self,
         settings: &ResolvedStepSettings,
     ) -> Option<ReasoningEffort> {
         if !self
             .services
             .model_client
-            .reasoning_effort_override_enabled()
-            || !settings.model_info.use_responses_lite
-            || !self.provider().await.is_openai()
+            .reasoning_effort_override_enabled(&settings.model_info)
         {
             return None;
         }
diff --git a/codex-rs/core/src/session/reasoning_effort_tests.rs b/codex-rs/core/src/session/reasoning_effort_tests.rs
index 2b8ce76afc..bee5f9f2a3 100644
--- a/codex-rs/core/src/session/reasoning_effort_tests.rs
+++ b/codex-rs/core/src/session/reasoning_effort_tests.rs
@@ -33,7 +33,7 @@ async fn initial_replay_preserves_prewarmed_effort(history: InitialHistory) {
     )
     .await;
     let mut model_info = Arc::clone(&turn_context.initial_settings.model_info);
-    Arc::make_mut(&mut model_info).use_responses_lite = true;
+    Arc::make_mut(&mut model_info).supports_reasoning_effort_updates = true;
     let mut selected = turn_context.initial_settings.selected().clone();
     selected.collaboration_mode.settings.reasoning_effort = Some(ReasoningEffort::Medium);
     let prewarm_settings = ResolvedStepSettings::new(
@@ -87,7 +87,7 @@ async fn compaction_effort_lookup_preserves_pin_for_fallback_models() {
     let effort = ReasoningEffort::Medium;
     let model = Arc::make_mut(&mut settings.model_info);
     model.slug = "fallback".to_string();
-    model.use_responses_lite = true;
+    model.supports_reasoning_effort_updates = true;
     model.default_reasoning_level = Some(effort.clone());
 
     assert_eq!(
@@ -106,3 +106,57 @@ async fn compaction_effort_lookup_preserves_pin_for_fallback_models() {
         Some(ReasoningEffort::Low)
     );
 }
+
+#[tokio::test]
+async fn unsupported_model_compaction_uses_selected_effort_without_mutating_pin() {
+    let (session, turn_context, _events) = make_session_and_context_with_auth_and_config_and_rx(
+        CodexAuth::from_api_key("Test API Key"),
+        Vec::new(),
+        |config| {
+            config
+                .features
+                .enable(Feature::ReasoningEffortOverride)
+                .unwrap();
+            config.model_reasoning_effort = Some(ReasoningEffort::High);
+        },
+    )
+    .await;
+    let mut settings = (*turn_context.initial_settings).clone();
+    Arc::make_mut(&mut settings.model_info).supports_reasoning_effort_updates = false;
+    session
+        .state
+        .lock()
+        .await
+        .reasoning_effort_pin
+        .pin(&settings.model_info.slug, ReasoningEffort::Low);
+
+    assert_eq!(
+        session
+            .reasoning_effort_for_request(&settings, RequestEffortUsage::Compaction)
+            .await,
+        Some(ReasoningEffort::High),
+    );
+    assert_eq!(
+        session
+            .state
+            .lock()
+            .await
+            .reasoning_effort_pin
+            .get(&settings.model_info.slug),
+        Some(ReasoningEffort::Low),
+    );
+    // Sampling retires the old baseline, so a later supported request starts afresh.
+    assert_eq!(
+        session
+            .reasoning_effort_for_request(&settings, RequestEffortUsage::Sampling)
+            .await,
+        Some(ReasoningEffort::High),
+    );
+    Arc::make_mut(&mut settings.model_info).supports_reasoning_effort_updates = true;
+    assert_eq!(
+        session
+            .reasoning_effort_for_request(&settings, RequestEffortUsage::Sampling)
+            .await,
+        Some(ReasoningEffort::High),
+    );
+}
diff --git a/codex-rs/core/tests/suite/auto_review.rs b/codex-rs/core/tests/suite/auto_review.rs
index 7f6b1a6eb2..6f5c9fc7d9 100644
--- a/codex-rs/core/tests/suite/auto_review.rs
+++ b/codex-rs/core/tests/suite/auto_review.rs
@@ -615,6 +615,7 @@ fn remote_model_with_auto_review_override(slug: &str, review_model: &str) -> Mod
         supports_search_tool: false,
         supports_experimental_context: false,
         use_responses_lite: false,
+        supports_reasoning_effort_updates: false,
         node_repl_auto_review_required: false,
         node_repl_disabled: false,
         auto_review_model_override: Some(review_model.to_string()),
diff --git a/codex-rs/core/tests/suite/compact.rs b/codex-rs/core/tests/suite/compact.rs
index 2beb7f554a..cfbcefc9d8 100644
--- a/codex-rs/core/tests/suite/compact.rs
+++ b/codex-rs/core/tests/suite/compact.rs
@@ -1038,6 +1038,7 @@ async fn reasoning_effort_override_remote_v2_compaction_resets_pinned_effort(
         .with_auth(CodexAuth::create_dummy_chatgpt_auth_for_testing())
         .with_model_info_override("gpt-5.4", |model| {
             model.use_responses_lite = true;
+            model.supports_reasoning_effort_updates = true;
         })
         .with_config(move |config| {
             config.model_provider.stream_max_retries = Some(0);
diff --git a/codex-rs/core/tests/suite/model_switching.rs b/codex-rs/core/tests/suite/model_switching.rs
index cebe8ff426..97a39d9a28 100644
--- a/codex-rs/core/tests/suite/model_switching.rs
+++ b/codex-rs/core/tests/suite/model_switching.rs
@@ -126,6 +126,7 @@ fn test_model_info(
         supports_search_tool: false,
         supports_experimental_context: false,
         use_responses_lite: false,
+        supports_reasoning_effort_updates: false,
         guardian: None,
         node_repl_auto_review_required: false,
         node_repl_disabled: false,
@@ -1253,6 +1254,7 @@ async fn model_switch_to_smaller_model_updates_token_context_window() -> Result<
         supports_search_tool: false,
         supports_experimental_context: false,
         use_responses_lite: false,
+        supports_reasoning_effort_updates: false,
         guardian: None,
         node_repl_auto_review_required: false,
         node_repl_disabled: false,
diff --git a/codex-rs/core/tests/suite/models_cache_ttl.rs b/codex-rs/core/tests/suite/models_cache_ttl.rs
index 3cba8b6eff..4a3cf558c1 100644
--- a/codex-rs/core/tests/suite/models_cache_ttl.rs
+++ b/codex-rs/core/tests/suite/models_cache_ttl.rs
@@ -679,6 +679,7 @@ fn test_remote_model(slug: &str, priority: i32) -> ModelInfo {
         supports_search_tool: false,
         supports_experimental_context: false,
         use_responses_lite: false,
+        supports_reasoning_effort_updates: false,
         guardian: None,
         node_repl_auto_review_required: false,
         node_repl_disabled: false,
diff --git a/codex-rs/core/tests/suite/reasoning_effort_override.rs b/codex-rs/core/tests/suite/reasoning_effort_override.rs
index 0099d94d28..ca317492fe 100644
--- a/codex-rs/core/tests/suite/reasoning_effort_override.rs
+++ b/codex-rs/core/tests/suite/reasoning_effort_override.rs
@@ -43,6 +43,7 @@ fn override_builder() -> TestCodexBuilder {
     test_codex()
         .with_model_info_override("gpt-5.4", |model| {
             model.use_responses_lite = true;
+            model.supports_reasoning_effort_updates = true;
         })
         .with_config(|config| {
             config
@@ -354,9 +355,12 @@ async fn reasoning_effort_override_persistent_transitions(
     Ok(())
 }
 
+#[test_case(true; "responses lite")]
+#[test_case(false; "ordinary responses")]
 #[tokio::test(flavor = "multi_thread", worker_threads = 2)]
-async fn reasoning_effort_override_preserves_prefix_and_only_appends_on_change()
--> anyhow::Result<()> {
+async fn reasoning_effort_override_preserves_prefix_and_only_appends_on_change(
+    use_responses_lite: bool,
+) -> anyhow::Result<()> {
     skip_if_no_network!(Ok(()));
     let server = responses::start_mock_server().await;
     let mut mocks = Vec::new();
@@ -366,7 +370,12 @@ async fn reasoning_effort_override_preserves_prefix_and_only_appends_on_change()
                 .await,
         );
     }
-    let test = override_builder().build_with_auto_env(&server).await?;
+    let test = override_builder()
+        .with_model_info_override("gpt-5.4", move |model| {
+            model.use_responses_lite = use_responses_lite;
+        })
+        .build_with_auto_env(&server)
+        .await?;
     test.submit_text_turn("first message").await?;
     submit_thread_settings(
         &test.codex,
@@ -718,8 +727,12 @@ async fn reasoning_effort_override_websocket_appends_then_replays_after_reconnec
     Ok(())
 }
 
+#[test_case(OverrideUnavailable::FeatureDisabled; "feature disabled")]
+#[test_case(OverrideUnavailable::ModelUnsupported; "unsupported model")]
 #[tokio::test(flavor = "multi_thread", worker_threads = 2)]
-async fn reasoning_effort_override_disabled_filters_websocket_history() -> anyhow::Result<()> {
+async fn reasoning_effort_override_unavailable_filters_websocket_history(
+    unavailable: OverrideUnavailable,
+) -> anyhow::Result<()> {
     skip_if_no_network!(Ok(()));
     let server = responses::start_mock_server().await;
     let initial_mock = responses::mount_sse_once(
@@ -747,11 +760,7 @@ async fn reasoning_effort_override_disabled_filters_websocket_history() -> anyho
     ]])
     .await;
     let base_url = format!("{}/v1", websocket.uri());
-    let mut builder = override_builder().with_config(move |config| {
-        config
-            .features
-            .disable(Feature::ReasoningEffortOverride)
-            .expect("disable overrides");
+    let mut builder = unavailable.builder().with_config(move |config| {
         config.model_reasoning_effort = Some(ReasoningEffort::High);
         config.model_provider.base_url = Some(base_url);
         config.model_provider.supports_websockets = true;
@@ -788,12 +797,33 @@ async fn reasoning_effort_override_disabled_filters_websocket_history() -> anyho
 enum OverrideUnavailable {
     FeatureDisabled,
     NonOpenAiProvider,
-    ResponsesLiteDisabled,
+    ModelUnsupported,
+}
+
+impl OverrideUnavailable {
+    fn builder(self) -> TestCodexBuilder {
+        match self {
+            Self::FeatureDisabled => override_builder().with_config(|config| {
+                config
+                    .features
+                    .disable(Feature::ReasoningEffortOverride)
+                    .expect("disable overrides");
+            }),
+            Self::NonOpenAiProvider => override_builder().with_config(|config| {
+                config.model_provider.name = "unsupported provider".into();
+            }),
+            Self::ModelUnsupported => {
+                override_builder().with_model_info_override("gpt-5.4", |model| {
+                    model.supports_reasoning_effort_updates = false;
+                })
+            }
+        }
+    }
 }
 
 #[test_case(OverrideUnavailable::FeatureDisabled; "feature disabled")]
 #[test_case(OverrideUnavailable::NonOpenAiProvider; "unsupported provider")]
-#[test_case(OverrideUnavailable::ResponsesLiteDisabled; "responses lite disabled")]
+#[test_case(OverrideUnavailable::ModelUnsupported; "unsupported model")]
 #[tokio::test(flavor = "multi_thread", worker_threads = 2)]
 async fn reasoning_effort_override_unavailable_uses_request_effort(
     unavailable: OverrideUnavailable,
@@ -810,20 +840,7 @@ async fn reasoning_effort_override_unavailable_uses_request_effort(
         responses::sse(vec![responses::ev_completed("second")]),
     )
     .await;
-    let mut builder = match unavailable {
-        OverrideUnavailable::FeatureDisabled => override_builder().with_config(|config| {
-            config
-                .features
-                .disable(Feature::ReasoningEffortOverride)
-                .expect("disable overrides");
-        }),
-        OverrideUnavailable::NonOpenAiProvider => override_builder().with_config(|config| {
-            config.model_provider.name = "unsupported provider".into();
-        }),
-        OverrideUnavailable::ResponsesLiteDisabled => override_builder()
-            .with_model_info_override("gpt-5.4", |model| model.use_responses_lite = false),
-    };
-    let test = builder.build_with_auto_env(&server).await?;
+    let test = unavailable.builder().build_with_auto_env(&server).await?;
     test.submit_text_turn("first").await?;
     submit_thread_settings(
         &test.codex,
@@ -846,8 +863,12 @@ async fn reasoning_effort_override_unavailable_uses_request_effort(
     Ok(())
 }
 
+#[test_case(OverrideUnavailable::FeatureDisabled; "feature disabled")]
+#[test_case(OverrideUnavailable::ModelUnsupported; "unsupported model")]
 #[tokio::test(flavor = "multi_thread", worker_threads = 2)]
-async fn reasoning_effort_override_disabled_recovers_saved_history() -> anyhow::Result<()> {
+async fn reasoning_effort_override_unavailable_recovers_saved_history(
+    unavailable: OverrideUnavailable,
+) -> anyhow::Result<()> {
     skip_if_no_network!(Ok(()));
     let server = responses::start_mock_server().await;
     let reply = |id, text| {
@@ -891,13 +912,10 @@ async fn reasoning_effort_override_disabled_recovers_saved_history() -> anyhow::
     })
     .await;
     let chatgpt_base_url = format!("{}/backend-api", server.uri());
-    let mut builder = override_builder()
+    let mut builder = unavailable
+        .builder()
         .with_auth(CodexAuth::create_dummy_chatgpt_auth_for_testing())
         .with_config(move |config| {
-            config
-                .features
-                .disable(Feature::ReasoningEffortOverride)
-                .expect("disable overrides");
             config.model_reasoning_effort = Some(ReasoningEffort::High);
             config.chatgpt_base_url = chatgpt_base_url;
         });
@@ -984,6 +1002,7 @@ async fn reasoning_effort_override_model_switch_reestablishes_selected_effort(
         .with_model_info_override("gpt-5.5", |model| {
             model.comp_hash = None;
             model.use_responses_lite = true;
+            model.supports_reasoning_effort_updates = true;
         })
         .with_model("gpt-5.4")
         .build_with_auto_env(&server)
@@ -1021,6 +1040,145 @@ async fn reasoning_effort_override_model_switch_reestablishes_selected_effort(
     Ok(())
 }
 
+#[tokio::test(flavor = "multi_thread", worker_threads = 2)]
+async fn reasoning_effort_override_unsupported_model_round_trip() -> anyhow::Result<()> {
+    skip_if_no_network!(Ok(()));
+    let server = responses::start_mock_server().await;
+    let test = override_builder()
+        .with_model_info_override("gpt-6-astra", |model| {
+            model.comp_hash = None;
+            model.use_responses_lite = true;
+            model.supports_reasoning_effort_updates = true;
+        })
+        .with_model_info_override("gpt-5.5", |model| {
+            model.comp_hash = None;
+            // Lite alone is not sufficient: unsupported models must still filter updates.
+            model.use_responses_lite = true;
+            model.supports_reasoning_effort_updates = false;
+        })
+        .with_model("gpt-6-astra")
+        .build_with_auto_env(&server)
+        .await?;
+    let turns = [
+        ("gpt-6-astra", ReasoningEffort::Medium, "Start at medium."),
+        (
+            "gpt-6-astra",
+            ReasoningEffort::High,
+            "Raise effort to high.",
+        ),
+        (
+            "gpt-5.5",
+            ReasoningEffort::High,
+            "Switch to the unsupported model.",
+        ),
+        ("gpt-5.5", ReasoningEffort::Low, "Lower effort to low."),
+        (
+            "gpt-6-astra",
+            ReasoningEffort::Low,
+            "Return to the supported model.",
+        ),
+        ("gpt-6-astra", ReasoningEffort::High, "Raise effort again."),
+    ];
+    let mut requests = Vec::new();
+    for (index, (model, effort, prompt)) in turns.iter().enumerate() {
+        let id = format!("turn-{index}");
+        let mock = responses::mount_sse_once(
+            &server,
+            responses::sse(vec![
+                responses::ev_assistant_message(&id, "Acknowledged."),
+                responses::ev_completed(&id),
+            ]),
+        )
+        .await;
+        submit_thread_settings(
+            &test.codex,
+            ThreadSettingsOverrides {
+                model: Some((*model).to_string()),
+                effort: Some(Some(effort.clone())),
+                ..Default::default()
+            },
+        )
+        .await?;
+        test.submit_text_turn(prompt).await?;
+        requests.push(mock.single_request());
+    }
+    let initial_updates = vec![
+        effort_update(ReasoningEffort::Medium),
+        effort_update(ReasoningEffort::High),
+    ];
+    let mut returned_updates = initial_updates.clone();
+    returned_updates.push(effort_update(ReasoningEffort::Low));
+    let mut final_updates = returned_updates.clone();
+    final_updates.push(effort_update(ReasoningEffort::High));
+    assert_eq!(
+        requests
+            .iter()
+            .map(|request| {
+                let body = request.body_json();
+                (
+                    body["model"].clone(),
+                    body["reasoning"]["effort"].clone(),
+                    effort_updates(request),
+                )
+            })
+            .collect::<Vec<_>>(),
+        vec![
+            (
+                Value::from("gpt-6-astra"),
+                Value::from("medium"),
+                vec![effort_update(ReasoningEffort::Medium)]
+            ),
+            (
+                Value::from("gpt-6-astra"),
+                Value::from("medium"),
+                initial_updates
+            ),
+            (Value::from("gpt-5.5"), Value::from("high"), vec![]),
+            (Value::from("gpt-5.5"), Value::from("low"), vec![]),
+            (
+                Value::from("gpt-6-astra"),
+                Value::from("low"),
+                returned_updates
+            ),
+            (
+                Value::from("gpt-6-astra"),
+                Value::from("low"),
+                final_updates.clone()
+            ),
+        ],
+    );
+    for (index, request) in requests.iter().enumerate() {
+        assert_eq!(
+            request
+                .message_input_texts("user")
+                .into_iter()
+                .filter(|text| { turns.iter().any(|(_, _, prompt)| text.as_str() == *prompt) })
+                .collect::<Vec<_>>(),
+            turns[..=index]
+                .iter()
+                .map(|(_, _, prompt)| prompt.to_string())
+                .collect::<Vec<_>>(),
+        );
+    }
+    test.codex.shutdown_and_wait().await?;
+    let saved_updates = test
+        .codex
+        .load_history(/*include_archived*/ false)
+        .await?
+        .items
+        .into_iter()
+        .filter_map(|item| match item {
+            RolloutItem::ResponseItem(ResponseItemEnvelope {
+                item: item @ ResponseItem::ConfigurationUpdate { .. },
+                ..
+            }) => Some(serde_json::to_value(item).expect("serialize saved update")),
+            _ => None,
+        })
+        .collect::<Vec<_>>();
+    assert_eq!(saved_updates, final_updates);
+    Ok(())
+}
+
 #[test_case(ReasoningEffort::High; "unchanged effort")]
 #[test_case(ReasoningEffort::Medium; "changed effort")]
 #[tokio::test(flavor = "multi_thread", worker_threads = 2)]
@@ -1129,6 +1287,7 @@ async fn reasoning_effort_override_compaction_fallback_uses_each_models_effort()
         .with_model_info_override("gpt-5.2", |model| {
             model.comp_hash = Some("fallback".to_string());
             model.use_responses_lite = true;
+            model.supports_reasoning_effort_updates = true;
         })
         .with_model("gpt-5.4")
         .with_config(move |config| {
diff --git a/codex-rs/core/tests/suite/remote_models.rs b/codex-rs/core/tests/suite/remote_models.rs
index 0568116770..b5a652c5a9 100644
--- a/codex-rs/core/tests/suite/remote_models.rs
+++ b/codex-rs/core/tests/suite/remote_models.rs
@@ -584,6 +584,7 @@ async fn remote_models_remote_model_uses_unified_exec() -> Result<()> {
         supports_search_tool: false,
         supports_experimental_context: false,
         use_responses_lite: false,
+        supports_reasoning_effort_updates: false,
         guardian: None,
         node_repl_auto_review_required: false,
         node_repl_disabled: false,
@@ -858,6 +859,7 @@ async fn remote_models_apply_legacy_instructions(auth: CodexAuth) -> Result<()>
         supports_search_tool: false,
         supports_experimental_context: false,
         use_responses_lite: false,
+        supports_reasoning_effort_updates: false,
         guardian: None,
         node_repl_auto_review_required: false,
         node_repl_disabled: false,
@@ -1440,6 +1442,7 @@ fn test_remote_model_with_policy(
         supports_search_tool: false,
         supports_experimental_context: false,
         use_responses_lite: false,
+        supports_reasoning_effort_updates: false,
         guardian: None,
         node_repl_auto_review_required: false,
         node_repl_disabled: false,
diff --git a/codex-rs/core/tests/suite/rmcp_client.rs b/codex-rs/core/tests/suite/rmcp_client.rs
index 2bb9eee369..714b305f5b 100644
--- a/codex-rs/core/tests/suite/rmcp_client.rs
+++ b/codex-rs/core/tests/suite/rmcp_client.rs
@@ -3008,6 +3008,7 @@ async fn stdio_image_responses_are_sanitized_for_text_only_model() -> anyhow::Re
                 supports_search_tool: false,
                 supports_experimental_context: false,
                 use_responses_lite: false,
+                supports_reasoning_effort_updates: false,
                 guardian: None,
                 node_repl_auto_review_required: false,
                 node_repl_disabled: false,
diff --git a/codex-rs/core/tests/suite/spawn_agent_description.rs b/codex-rs/core/tests/suite/spawn_agent_description.rs
index 2df387602f..bc0eaf7580 100644
--- a/codex-rs/core/tests/suite/spawn_agent_description.rs
+++ b/codex-rs/core/tests/suite/spawn_agent_description.rs
@@ -92,6 +92,7 @@ fn test_model_info(
         supports_search_tool: false,
         supports_experimental_context: false,
         use_responses_lite: false,
+        supports_reasoning_effort_updates: false,
         guardian: None,
         node_repl_auto_review_required: false,
         node_repl_disabled: false,
diff --git a/codex-rs/core/tests/suite/view_image.rs b/codex-rs/core/tests/suite/view_image.rs
index e29c41d6cd..62479ce0e6 100644
--- a/codex-rs/core/tests/suite/view_image.rs
+++ b/codex-rs/core/tests/suite/view_image.rs
@@ -1624,6 +1624,7 @@ async fn view_image_tool_returns_unsupported_message_for_text_only_model() -> an
         supports_search_tool: false,
         supports_experimental_context: false,
         use_responses_lite: false,
+        supports_reasoning_effort_updates: false,
         guardian: None,
         node_repl_auto_review_required: false,
         node_repl_disabled: false,
diff --git a/codex-rs/models-manager/src/model_info.rs b/codex-rs/models-manager/src/model_info.rs
index ece19ad26a..88ade7cfcf 100644
--- a/codex-rs/models-manager/src/model_info.rs
+++ b/codex-rs/models-manager/src/model_info.rs
@@ -137,6 +137,7 @@ pub fn model_info_from_slug(slug: &str) -> ModelInfo {
         supports_search_tool: false,
         supports_experimental_context: false,
         use_responses_lite: false,
+        supports_reasoning_effort_updates: false,
         guardian: None,
         node_repl_auto_review_required: false,
         node_repl_disabled: false,
diff --git a/codex-rs/prompts/src/model_instructions_tests.rs b/codex-rs/prompts/src/model_instructions_tests.rs
index 9fa9bb5879..540cbabc79 100644
--- a/codex-rs/prompts/src/model_instructions_tests.rs
+++ b/codex-rs/prompts/src/model_instructions_tests.rs
@@ -48,6 +48,7 @@ fn test_model(model_messages: Option<ModelMessages>) -> ModelInfo {
         supports_search_tool: false,
         supports_experimental_context: false,
         use_responses_lite: false,
+        supports_reasoning_effort_updates: false,
         guardian: None,
         node_repl_auto_review_required: false,
         node_repl_disabled: false,
diff --git a/codex-rs/protocol/src/openai_models.rs b/codex-rs/protocol/src/openai_models.rs
index f52a4e601b..41b2a60dd5 100644
--- a/codex-rs/protocol/src/openai_models.rs
+++ b/codex-rs/protocol/src/openai_models.rs
@@ -481,6 +481,10 @@ pub struct ModelInfo {
     pub supports_experimental_context: bool,
     #[serde(default)]
     pub use_responses_lite: bool,
+    /// Whether the model accepts reasoning-effort `configuration_update` items.
+    /// Missing metadata keeps effort changes on the ordinary request parameter.
+    #[serde(default)]
+    pub supports_reasoning_effort_updates: bool,
     #[serde(default)]
     pub node_repl_auto_review_required: bool,
     #[serde(default)]
@@ -989,6 +993,7 @@ mod tests {
             supports_search_tool: false,
             supports_experimental_context: false,
             use_responses_lite: false,
+            supports_reasoning_effort_updates: false,
             guardian: None,
             node_repl_auto_review_required: false,
             node_repl_disabled: false,
@@ -1543,6 +1548,7 @@ mod tests {
         assert!(!model.supports_search_tool);
         assert!(!model.supports_experimental_context);
         assert!(!model.use_responses_lite);
+        assert!(!model.supports_reasoning_effort_updates);
         assert!(!model.node_repl_auto_review_required);
         assert!(!model.node_repl_disabled);
         assert_eq!(model.comp_hash, None);