diff --git a/codex-rs/core/src/exec_env.rs b/codex-rs/core/src/exec_env.rs
index 4daa29eb0c..056c1cef1b 100644
--- a/codex-rs/core/src/exec_env.rs
+++ b/codex-rs/core/src/exec_env.rs
@@ -13,6 +13,8 @@ use std::collections::HashMap;
 pub use codex_protocol::shell_environment::CODEX_SESSION_ID_ENV_VAR;
 pub use codex_protocol::shell_environment::CODEX_THREAD_ID_ENV_VAR;
 
+pub(crate) const CODEX_VERSION_ENV_VAR: &str = "CODEX_VERSION";
+
 /// Informational name of the active permission profile. Child processes can
 /// overwrite this value, so it must not be treated as proof of enforcement.
 pub const CODEX_PERMISSION_PROFILE_ENV_VAR: &str = "CODEX_PERMISSION_PROFILE";
@@ -35,9 +37,16 @@ pub fn create_env(
     shell_environment::create_env(policy, thread_id.as_deref())
 }
 
-/// Exposes the shared root-session identity to model-reachable shell commands.
-pub(crate) fn inject_session_id_env(env: &mut HashMap<String, String>, session_id: SessionId) {
+/// Exposes the shared root-session identity and harness version to shell commands.
+pub(crate) fn inject_session_env(env: &mut HashMap<String, String>, session_id: SessionId) {
     env.insert(CODEX_SESSION_ID_ENV_VAR.to_string(), session_id.to_string());
+    if cfg!(windows) {
+        env.retain(|key, _| !key.eq_ignore_ascii_case(CODEX_VERSION_ENV_VAR));
+    }
+    env.insert(
+        CODEX_VERSION_ENV_VAR.to_string(),
+        env!("CARGO_PKG_VERSION").to_string(),
+    );
 }
 
 /// Injects the selected named permission profile into a shell tool's environment.
diff --git a/codex-rs/core/src/tasks/user_shell.rs b/codex-rs/core/src/tasks/user_shell.rs
index 7d72cde569..ad7097126e 100644
--- a/codex-rs/core/src/tasks/user_shell.rs
+++ b/codex-rs/core/src/tasks/user_shell.rs
@@ -15,7 +15,7 @@ use crate::exec::StdoutStream;
 use crate::exec::execute_exec_request;
 use crate::exec_env::create_env;
 use crate::exec_env::inject_apply_patch_env;
-use crate::exec_env::inject_session_id_env;
+use crate::exec_env::inject_session_env;
 use crate::sandboxing::ExecRequest;
 use crate::session::TurnInput;
 use crate::session::turn_context::TurnContext;
@@ -166,7 +166,7 @@ pub(crate) async fn execute_user_shell_command(
     let shell_snapshot_location = turn_environment.shell_snapshot(&cwd);
     let shell_environment_policy = turn_environment.shell_environment_policy();
     let mut exec_env_map = create_env(shell_environment_policy, Some(session.thread_id));
-    inject_session_id_env(&mut exec_env_map, session.session_id());
+    inject_session_env(&mut exec_env_map, session.session_id());
     inject_apply_patch_env(&mut exec_env_map, &turn_context.config.features);
     if exec_env_map.contains_key(PROXY_ACTIVE_ENV_KEY) {
         strip_managed_proxy_env(&mut exec_env_map);
diff --git a/codex-rs/core/src/tools/runtimes/mod.rs b/codex-rs/core/src/tools/runtimes/mod.rs
index 3dc7e18526..9f4b2063b2 100644
--- a/codex-rs/core/src/tools/runtimes/mod.rs
+++ b/codex-rs/core/src/tools/runtimes/mod.rs
@@ -7,6 +7,7 @@ small and focused and reuses the orchestrator for approvals + sandbox + retry.
 use crate::exec_env::CODEX_PERMISSION_PROFILE_ENV_VAR;
 use crate::exec_env::CODEX_SESSION_ID_ENV_VAR;
 use crate::exec_env::CODEX_THREAD_ID_ENV_VAR;
+use crate::exec_env::CODEX_VERSION_ENV_VAR;
 use crate::sandboxing::SandboxPermissions;
 use crate::shell::Shell;
 use crate::shell::ShellType;
@@ -264,6 +265,7 @@ pub(crate) fn maybe_wrap_shell_lc_with_snapshot(
     for key in [
         CODEX_SESSION_ID_ENV_VAR,
         CODEX_THREAD_ID_ENV_VAR,
+        CODEX_VERSION_ENV_VAR,
         CODEX_PERMISSION_PROFILE_ENV_VAR,
         CODEX_APPLY_PATCH_PRESERVE_LINE_ENDINGS_ENV_VAR,
         PLUGIN_METRICS_OUTPUT_ENV_VAR,
diff --git a/codex-rs/core/src/tools/runtimes/mod_tests.rs b/codex-rs/core/src/tools/runtimes/mod_tests.rs
index d978777f40..d2a3292d54 100644
--- a/codex-rs/core/src/tools/runtimes/mod_tests.rs
+++ b/codex-rs/core/src/tools/runtimes/mod_tests.rs
@@ -494,12 +494,12 @@ fn maybe_wrap_shell_lc_with_snapshot_restores_explicit_override_precedence() {
 }
 
 #[test]
-fn maybe_wrap_shell_lc_with_snapshot_restores_codex_thread_id_from_env() {
+fn maybe_wrap_shell_lc_with_snapshot_restores_codex_metadata_from_env() {
     let dir = tempdir().expect("create temp dir");
     let snapshot_path = dir.path().join("snapshot.sh");
     std::fs::write(
         &snapshot_path,
-        "# Snapshot file\nexport CODEX_THREAD_ID='parent-thread'\n",
+        "# Snapshot file\nexport CODEX_THREAD_ID='parent-thread'\nexport CODEX_VERSION='old-version'\n",
     )
     .expect("write snapshot");
     let (session_shell, shell_snapshot) =
@@ -507,24 +507,34 @@ fn maybe_wrap_shell_lc_with_snapshot_restores_codex_thread_id_from_env() {
     let command = vec![
         "/bin/bash".to_string(),
         "-lc".to_string(),
-        "printf '%s' \"$CODEX_THREAD_ID\"".to_string(),
+        "printf '%s|%s' \"$CODEX_THREAD_ID\" \"$CODEX_VERSION\"".to_string(),
     ];
+    let env = HashMap::from([
+        ("CODEX_THREAD_ID".to_string(), "nested-thread".to_string()),
+        (
+            "CODEX_VERSION".to_string(),
+            env!("CARGO_PKG_VERSION").to_string(),
+        ),
+    ]);
     let rewritten = maybe_wrap_shell_lc_with_snapshot(
         &command,
         &session_shell,
         Some(&shell_snapshot),
         &HashMap::new(),
-        &HashMap::from([("CODEX_THREAD_ID".to_string(), "nested-thread".to_string())]),
+        &env,
         &RuntimePathPrepends::default(),
     );
     let output = Command::new(&rewritten[0])
         .args(&rewritten[1..])
-        .env("CODEX_THREAD_ID", "nested-thread")
+        .envs(env)
         .output()
         .expect("run rewritten command");
 
     assert!(output.status.success(), "command failed: {output:?}");
-    assert_eq!(String::from_utf8_lossy(&output.stdout), "nested-thread");
+    assert_eq!(
+        String::from_utf8_lossy(&output.stdout),
+        concat!("nested-thread|", env!("CARGO_PKG_VERSION")),
+    );
 }
 
 #[test]
diff --git a/codex-rs/core/src/turn_metadata.rs b/codex-rs/core/src/turn_metadata.rs
index 56d962c1fc..8d3114845c 100644
--- a/codex-rs/core/src/turn_metadata.rs
+++ b/codex-rs/core/src/turn_metadata.rs
@@ -45,6 +45,7 @@ use codex_utils_git_discovery::GitRootDiscovery;
 const MEMORY_GIT_METADATA_TIMEOUT: std::time::Duration = std::time::Duration::from_secs(1);
 
 const MODEL_KEY: &str = "model";
+const CODEX_VERSION_KEY: &str = "codex_version";
 const REASONING_EFFORT_KEY: &str = "reasoning_effort";
 const USER_INPUT_REQUESTED_DURING_TURN_KEY: &str = "user_input_requested_during_turn";
 const WORKSPACE_KIND_KEY: &str = "workspace_kind";
@@ -246,6 +247,10 @@ impl TurnMetadataState {
             MODEL_KEY.to_string(),
             Value::String(context.model.to_string()),
         );
+        metadata.insert(
+            CODEX_VERSION_KEY.to_string(),
+            Value::String(env!("CARGO_PKG_VERSION").to_string()),
+        );
         match context.reasoning_effort {
             Some(reasoning_effort) => {
                 metadata.insert(
diff --git a/codex-rs/core/src/turn_metadata_tests.rs b/codex-rs/core/src/turn_metadata_tests.rs
index 64cb45b8d7..247b01c47f 100644
--- a/codex-rs/core/src/turn_metadata_tests.rs
+++ b/codex-rs/core/src/turn_metadata_tests.rs
@@ -739,6 +739,7 @@ fn turn_metadata_state_merges_client_metadata_without_replacing_reserved_fields(
         ("workspace_kind".to_string(), "projectless".to_string()),
         ("source".to_string(), "client-source".to_string()),
         ("model".to_string(), "client-supplied".to_string()),
+        ("codex_version".to_string(), "client-supplied".to_string()),
         (
             "reasoning_effort".to_string(),
             "client-supplied".to_string(),
@@ -932,6 +933,7 @@ fn turn_metadata_state_merges_client_metadata_without_replacing_reserved_fields(
         .current_meta_value_for_mcp_request(test_mcp_turn_metadata_context())
         .expect("turn metadata should be present");
     assert_eq!(meta["model"].as_str(), Some("gpt-5.4"));
+    assert_eq!(meta["codex_version"], env!("CARGO_PKG_VERSION"));
     assert_eq!(meta["reasoning_effort"].as_str(), Some("high"));
     assert!(meta.get(LEGACY_CODE_MODE_TOOL_NAMES_KEY).is_none());
     assert!(meta.get(TOOL_NAMESPACES_INFO_KEY).is_none());
diff --git a/codex-rs/core/src/unified_exec/process_manager.rs b/codex-rs/core/src/unified_exec/process_manager.rs
index 81d91c73a4..5becfea9bc 100644
--- a/codex-rs/core/src/unified_exec/process_manager.rs
+++ b/codex-rs/core/src/unified_exec/process_manager.rs
@@ -17,10 +17,11 @@ use super::oneshot::Completion;
 use crate::codex_thread::BackgroundTerminalInfo;
 use crate::exec_env::CODEX_PERMISSION_PROFILE_ENV_VAR;
 use crate::exec_env::CODEX_THREAD_ID_ENV_VAR;
+use crate::exec_env::CODEX_VERSION_ENV_VAR;
 use crate::exec_env::create_env;
 use crate::exec_env::inject_apply_patch_env;
 use crate::exec_env::inject_permission_profile_env;
-use crate::exec_env::inject_session_id_env;
+use crate::exec_env::inject_session_env;
 use crate::exec_policy::ExecApprovalRequest;
 use crate::guardian::GuardianReviewContext;
 use crate::plugins::metrics::finish_and_track_measurements;
@@ -138,6 +139,7 @@ pub(super) fn exec_env_policy_from_shell_policy(
         .collect::<Vec<_>>();
     exclude.extend([
         CODEX_PERMISSION_PROFILE_ENV_VAR.to_string(),
+        CODEX_VERSION_ENV_VAR.to_string(),
         codex_apply_patch::CODEX_APPLY_PATCH_PRESERVE_LINE_ENDINGS_ENV_VAR.to_string(),
         PLUGIN_METRICS_OUTPUT_ENV_VAR.to_string(),
     ]);
@@ -145,6 +147,7 @@ pub(super) fn exec_env_policy_from_shell_policy(
     r#set.retain(|key, _| {
         ![
             CODEX_PERMISSION_PROFILE_ENV_VAR,
+            CODEX_VERSION_ENV_VAR,
             codex_apply_patch::CODEX_APPLY_PATCH_PRESERVE_LINE_ENDINGS_ENV_VAR,
             PLUGIN_METRICS_OUTPUT_ENV_VAR,
         ]
@@ -176,6 +179,7 @@ fn env_overlay_for_exec_server(
                 && (matches!(
                     key.as_str(),
                     CODEX_PERMISSION_PROFILE_ENV_VAR
+                        | CODEX_VERSION_ENV_VAR
                         | codex_apply_patch::CODEX_APPLY_PATCH_PRESERVE_LINE_ENDINGS_ENV_VAR
                 ) || local_policy_env.get(*key) != Some(*value))
         })
@@ -1362,7 +1366,7 @@ impl UnifiedExecProcessManager {
             CODEX_THREAD_ID_ENV_VAR.to_string(),
             context.session.thread_id.to_string(),
         );
-        inject_session_id_env(&mut env, context.session.session_id());
+        inject_session_env(&mut env, context.session.session_id());
         inject_apply_patch_env(&mut env, &turn.config.features);
         let active_permission_profile = request.turn_environment.active_permission_profile();
         inject_permission_profile_env(&mut env, active_permission_profile.as_ref());
diff --git a/codex-rs/core/src/unified_exec/process_manager_tests.rs b/codex-rs/core/src/unified_exec/process_manager_tests.rs
index c1103e569b..29f9e8839c 100644
--- a/codex-rs/core/src/unified_exec/process_manager_tests.rs
+++ b/codex-rs/core/src/unified_exec/process_manager_tests.rs
@@ -53,6 +53,10 @@ fn env_overlay_for_exec_server_keeps_runtime_changes_only() {
         ("HOME".to_string(), "/client-home".to_string()),
         ("PATH".to_string(), "/client-path".to_string()),
         ("SHELL_SET".to_string(), "policy".to_string()),
+        (
+            CODEX_VERSION_ENV_VAR.to_string(),
+            "client-version".to_string(),
+        ),
         (
             CODEX_PERMISSION_PROFILE_ENV_VAR.to_string(),
             "current-profile".to_string(),
@@ -68,6 +72,10 @@ fn env_overlay_for_exec_server_keeps_runtime_changes_only() {
         ("OpenAI_Federation_Rule_Id".to_string(), "rule".to_string()),
         ("SHELL_SET".to_string(), "policy".to_string()),
         ("CODEX_THREAD_ID".to_string(), "thread-1".to_string()),
+        (
+            CODEX_VERSION_ENV_VAR.to_string(),
+            "client-version".to_string(),
+        ),
         (
             CODEX_PERMISSION_PROFILE_ENV_VAR.to_string(),
             "current-profile".to_string(),
@@ -87,6 +95,10 @@ fn env_overlay_for_exec_server_keeps_runtime_changes_only() {
         HashMap::from([
             ("PATH".to_string(), "/sandbox-path".to_string()),
             ("CODEX_THREAD_ID".to_string(), "thread-1".to_string()),
+            (
+                CODEX_VERSION_ENV_VAR.to_string(),
+                "client-version".to_string()
+            ),
             (
                 CODEX_PERMISSION_PROFILE_ENV_VAR.to_string(),
                 "current-profile".to_string(),
@@ -107,6 +119,7 @@ fn env_overlay_for_exec_server_keeps_runtime_changes_only() {
 fn exec_env_policy_excludes_non_inheritable_and_runtime_variables() {
     let policy = ShellEnvironmentPolicy {
         r#set: HashMap::from([
+            ("codex_version".to_string(), "stale-version".to_string()),
             (
                 "codex_permission_profile".to_string(),
                 "stale-profile".to_string(),
@@ -135,6 +148,7 @@ fn exec_env_policy_excludes_non_inheritable_and_runtime_variables() {
             ignore_default_excludes: policy.ignore_default_excludes,
             exclude: vec![
                 CODEX_PERMISSION_PROFILE_ENV_VAR.to_string(),
+                CODEX_VERSION_ENV_VAR.to_string(),
                 codex_apply_patch::CODEX_APPLY_PATCH_PRESERVE_LINE_ENDINGS_ENV_VAR.to_string(),
                 PLUGIN_METRICS_OUTPUT_ENV_VAR.to_string(),
             ],
diff --git a/codex-rs/core/src/unified_exec/shell_snapshot.rs b/codex-rs/core/src/unified_exec/shell_snapshot.rs
index fdce56e3b3..c04b7d541e 100644
--- a/codex-rs/core/src/unified_exec/shell_snapshot.rs
+++ b/codex-rs/core/src/unified_exec/shell_snapshot.rs
@@ -23,7 +23,7 @@ use crate::config::NetworkProxySpec;
 use crate::exec_env::CODEX_THREAD_ID_ENV_VAR;
 use crate::exec_env::inject_apply_patch_env;
 use crate::exec_env::inject_permission_profile_env;
-use crate::exec_env::inject_session_id_env;
+use crate::exec_env::inject_session_env;
 use crate::session::session::Session;
 use crate::session::step_context::StepContext;
 use crate::shell::ShellType;
@@ -114,7 +114,7 @@ impl Session {
                     CODEX_THREAD_ID_ENV_VAR.to_string(),
                     session.thread_id().to_string(),
                 );
-                inject_session_id_env(&mut env, session.session_id());
+                inject_session_env(&mut env, session.session_id());
                 inject_apply_patch_env(&mut env, &config.features);
                 inject_permission_profile_env(
                     &mut env,
diff --git a/codex-rs/core/tests/suite/mcp_turn_metadata.rs b/codex-rs/core/tests/suite/mcp_turn_metadata.rs
index d3d5ecf07f..899e680921 100644
--- a/codex-rs/core/tests/suite/mcp_turn_metadata.rs
+++ b/codex-rs/core/tests/suite/mcp_turn_metadata.rs
@@ -527,6 +527,10 @@ async fn approved_mcp_tool_call_metadata_records_prior_user_input_request(
     let mcp_turn_metadata = apps_tool_call
         .pointer("/params/_meta/x-codex-turn-metadata")
         .expect("MCP tools/call turn metadata");
+    assert_eq!(
+        mcp_turn_metadata["codex_version"],
+        env!("CARGO_PKG_VERSION")
+    );
     assert_eq!(
         (
             mcp_turn_metadata.get("root_turn_id"),
diff --git a/codex-rs/core/tests/suite/unified_exec.rs b/codex-rs/core/tests/suite/unified_exec.rs
index 94cc55dd1f..1c9142dd3f 100644
--- a/codex-rs/core/tests/suite/unified_exec.rs
+++ b/codex-rs/core/tests/suite/unified_exec.rs
@@ -376,6 +376,10 @@ async fn exec_command_uses_installed_environment_shell_policy_with_explicit_over
             r#set: HashMap::from([
                 ("KEEP".to_string(), "preserved".to_string()),
                 ("DROP".to_string(), "filtered".to_string()),
+                (
+                    "CODEX_VERSION".to_string(),
+                    "configured-version".to_string(),
+                ),
             ]),
             ..Default::default()
         };
@@ -428,10 +432,10 @@ async fn exec_command_uses_installed_environment_shell_policy_with_explicit_over
     let call_id = "exec-command-environment-shell-policy";
     let command = match core_test_support::test_target_os() {
         core_test_support::TestTargetOs::Linux | core_test_support::TestTargetOs::MacOs => {
-            r#"printf '%s:%s:%s' "$KEEP" "${DROP:-missing}" "${OWNER_ONLY:-missing}""#
+            r#"printf '%s:%s:%s:%s' "$KEEP" "${DROP:-missing}" "${OWNER_ONLY:-missing}" "$CODEX_VERSION""#
         }
         core_test_support::TestTargetOs::Windows => {
-            r#"if (Test-Path Env:DROP) { $drop = $env:DROP } else { $drop = 'missing' }; if (Test-Path Env:OWNER_ONLY) { $owner = $env:OWNER_ONLY } else { $owner = 'missing' }; Write-Output "${env:KEEP}:${drop}:${owner}""#
+            r#"if (Test-Path Env:DROP) { $drop = $env:DROP } else { $drop = 'missing' }; if (Test-Path Env:OWNER_ONLY) { $owner = $env:OWNER_ONLY } else { $owner = 'missing' }; Write-Output "${env:KEEP}:${drop}:${owner}:${env:CODEX_VERSION}""#
         }
     };
     let arguments = json!({
@@ -462,7 +466,10 @@ async fn exec_command_uses_installed_environment_shell_policy_with_explicit_over
         )
         .await?;
     let output = parse_unified_exec_output(&harness.function_call_stdout(call_id).await)?;
-    assert_eq!(output.output.trim(), "preserved:missing:missing");
+    assert_eq!(
+        output.output.trim(),
+        concat!("preserved:missing:missing:", env!("CARGO_PKG_VERSION")),
+    );
     Ok(())
 }