diff --git a/codex-rs/app-server-protocol/src/protocol/v2.rs b/codex-rs/app-server-protocol/src/protocol/v2.rs
index 2ecaa733ed..9df301e878 100644
--- a/codex-rs/app-server-protocol/src/protocol/v2.rs
+++ b/codex-rs/app-server-protocol/src/protocol/v2.rs
@@ -3074,6 +3074,14 @@ pub struct ThreadStartParams {
     pub ephemeral: Option<bool>,
     #[ts(optional = nullable)]
     pub session_start_source: Option<ThreadStartSource>,
+    /// Optional sticky environment selections for this thread.
+    ///
+    /// Omitted uses EnvironmentManager default behavior. Empty disables
+    /// environment access for turns that do not provide a turn override.
+    /// Non-empty selects the first environment as the current turn environment.
+    #[experimental("thread/start.environments")]
+    #[ts(optional = nullable)]
+    pub environments: Option<Vec<TurnEnvironmentParams>>,
     #[experimental("thread/start.dynamicTools")]
     #[ts(optional = nullable)]
     pub dynamic_tools: Option<Vec<DynamicToolSpec>>,
@@ -4662,6 +4670,10 @@ pub struct TurnStartParams {
     #[ts(optional = nullable)]
     pub responsesapi_client_metadata: Option<HashMap<String, String>>,
     /// Optional turn-scoped environment selections.
+    ///
+    /// Omitted uses the thread sticky environment selections. Empty disables
+    /// environment access for this turn. Non-empty selects the first
+    /// environment as the current turn environment for this turn.
     #[experimental("turn/start.environments")]
     #[ts(optional = nullable)]
     pub environments: Option<Vec<TurnEnvironmentParams>>,
diff --git a/codex-rs/app-server/src/codex_message_processor.rs b/codex-rs/app-server/src/codex_message_processor.rs
index e5d815cbb4..8ff4de3e76 100644
--- a/codex-rs/app-server/src/codex_message_processor.rs
+++ b/codex-rs/app-server/src/codex_message_processor.rs
@@ -2353,8 +2353,18 @@ impl CodexMessageProcessor {
             personality,
             ephemeral,
             session_start_source,
+            environments,
             persist_extended_history,
         } = params;
+        let environments = environments.map(|environments| {
+            environments
+                .into_iter()
+                .map(|environment| TurnEnvironmentSelection {
+                    environment_id: environment.environment_id,
+                    cwd: environment.cwd,
+                })
+                .collect()
+        });
         let mut typesafe_overrides = self.build_thread_config_overrides(
             model,
             model_provider,
@@ -2392,6 +2402,7 @@ impl CodexMessageProcessor {
                 typesafe_overrides,
                 dynamic_tools,
                 session_start_source,
+                environments,
                 persist_extended_history,
                 service_name,
                 experimental_raw_events,
@@ -2466,6 +2477,7 @@ impl CodexMessageProcessor {
         typesafe_overrides: ConfigOverrides,
         dynamic_tools: Option<Vec<ApiDynamicToolSpec>>,
         session_start_source: Option<codex_app_server_protocol::ThreadStartSource>,
+        environment_selections: Option<Vec<TurnEnvironmentSelection>>,
         persist_extended_history: bool,
         service_name: Option<String>,
         experimental_raw_events: bool,
@@ -2613,6 +2625,7 @@ impl CodexMessageProcessor {
                 persist_extended_history,
                 service_name,
                 request_trace,
+                environment_selections,
             )
             .instrument(tracing::info_span!(
                 "app_server.thread_start.create_thread",
@@ -7219,6 +7232,7 @@ impl CodexMessageProcessor {
                         service_tier: params.service_tier,
                         collaboration_mode,
                         personality: params.personality,
+                        environments: None,
                     },
                 )
                 .await;
diff --git a/codex-rs/core/src/codex_delegate.rs b/codex-rs/core/src/codex_delegate.rs
index 858154eb77..ae7b717568 100644
--- a/codex-rs/core/src/codex_delegate.rs
+++ b/codex-rs/core/src/codex_delegate.rs
@@ -92,6 +92,7 @@ pub(crate) async fn run_codex_thread_interactive(
         user_shell_override: None,
         inherited_exec_policy: Some(Arc::clone(&parent_session.services.exec_policy)),
         parent_trace: None,
+        environment_selections: None,
         analytics_events_client: Some(parent_session.services.analytics_events_client.clone()),
     }))
     .await?;
diff --git a/codex-rs/core/src/session/handlers.rs b/codex-rs/core/src/session/handlers.rs
index 1751e7075d..108bb1cfe9 100644
--- a/codex-rs/core/src/session/handlers.rs
+++ b/codex-rs/core/src/session/handlers.rs
@@ -166,6 +166,7 @@ pub(super) async fn user_input_or_turn_inner(
                     personality,
                     app_server_client_name: None,
                     app_server_client_version: None,
+                    environment_selections: None,
                 },
                 None,
                 environments,
@@ -1077,6 +1078,7 @@ pub(super) async fn submission_loop(
                     service_tier,
                     collaboration_mode,
                     personality,
+                    environments,
                 } => {
                     let collaboration_mode = if let Some(collab_mode) = collaboration_mode {
                         collab_mode
@@ -1101,6 +1103,7 @@ pub(super) async fn submission_loop(
                             reasoning_summary: summary,
                             service_tier,
                             personality,
+                            environment_selections: environments,
                             ..Default::default()
                         },
                     )
diff --git a/codex-rs/core/src/session/mod.rs b/codex-rs/core/src/session/mod.rs
index cd6aca5dfe..4f27edb5bd 100644
--- a/codex-rs/core/src/session/mod.rs
+++ b/codex-rs/core/src/session/mod.rs
@@ -401,6 +401,7 @@ pub(crate) struct CodexSpawnArgs {
     pub(crate) inherited_exec_policy: Option<Arc<ExecPolicyManager>>,
     pub(crate) user_shell_override: Option<shell::Shell>,
     pub(crate) parent_trace: Option<W3cTraceContext>,
+    pub(crate) environment_selections: Option<Vec<TurnEnvironmentSelection>>,
     pub(crate) analytics_events_client: Option<AnalyticsEventsClient>,
 }
 
@@ -455,6 +456,7 @@ impl Codex {
             user_shell_override,
             inherited_exec_policy,
             parent_trace: _,
+            environment_selections,
             analytics_events_client,
         } = args;
         let (tx_sub, rx_sub) = async_channel::bounded(SUBMISSION_CHANNEL_CAPACITY);
@@ -617,6 +619,7 @@ impl Codex {
             cwd: config.cwd.clone(),
             codex_home: config.codex_home.clone(),
             thread_name: None,
+            environment_selections,
             original_config_do_not_use: Arc::clone(&config),
             metrics_service_name,
             app_server_client_name: None,
@@ -626,6 +629,7 @@ impl Codex {
             persist_extended_history,
             inherited_shell_snapshot,
             user_shell_override,
+            environment_selections,
         };
 
         // Generate a unique ID for the lifetime of this Codex session.
diff --git a/codex-rs/core/src/session/session.rs b/codex-rs/core/src/session/session.rs
index 0c8ab535f5..f33993b196 100644
--- a/codex-rs/core/src/session/session.rs
+++ b/codex-rs/core/src/session/session.rs
@@ -71,6 +71,9 @@ pub(crate) struct SessionConfiguration {
     pub(super) codex_home: AbsolutePathBuf,
     /// Optional user-facing name for the thread, updated during the session.
     pub(super) thread_name: Option<String>,
+    /// Sticky environment selections for turns that do not provide a turn-local override.
+    pub(super) environment_selections:
+        Option<Vec<codex_protocol::protocol::TurnEnvironmentSelection>>,
 
     // TODO(pakrym): Remove config from here
     pub(super) original_config_do_not_use: Arc<Config>,
@@ -181,6 +184,9 @@ impl SessionConfiguration {
         if let Some(app_server_client_version) = updates.app_server_client_version.clone() {
             next_configuration.app_server_client_version = Some(app_server_client_version);
         }
+        if let Some(environment_selections) = updates.environment_selections.clone() {
+            next_configuration.environment_selections = Some(environment_selections);
+        }
         Ok(next_configuration)
     }
 }
@@ -199,6 +205,8 @@ pub(crate) struct SessionSettingsUpdate {
     pub(crate) personality: Option<Personality>,
     pub(crate) app_server_client_name: Option<String>,
     pub(crate) app_server_client_version: Option<String>,
+    pub(crate) environment_selections:
+        Option<Vec<codex_protocol::protocol::TurnEnvironmentSelection>>,
 }
 
 pub(crate) struct AppServerClientMetadata {
diff --git a/codex-rs/core/src/session/tests.rs b/codex-rs/core/src/session/tests.rs
index 5d838e3db5..5855b62141 100644
--- a/codex-rs/core/src/session/tests.rs
+++ b/codex-rs/core/src/session/tests.rs
@@ -1688,6 +1688,7 @@ async fn fork_startup_context_then_first_turn_diff_snapshot() -> anyhow::Result<
             service_tier: None,
             collaboration_mode: Some(collaboration_mode),
             personality: None,
+            environments: None,
         })
         .await?;
 
@@ -2321,6 +2322,7 @@ async fn set_rate_limits_retains_previous_credits() {
         cwd: config.cwd.clone(),
         codex_home: config.codex_home.clone(),
         thread_name: None,
+        environment_selections: None,
         original_config_do_not_use: Arc::clone(&config),
         metrics_service_name: None,
         app_server_client_name: None,
@@ -2426,6 +2428,7 @@ async fn set_rate_limits_updates_plan_type_when_present() {
         cwd: config.cwd.clone(),
         codex_home: config.codex_home.clone(),
         thread_name: None,
+        environment_selections: None,
         original_config_do_not_use: Arc::clone(&config),
         metrics_service_name: None,
         app_server_client_name: None,
@@ -2781,6 +2784,7 @@ pub(crate) async fn make_session_configuration_for_tests() -> SessionConfigurati
         cwd: config.cwd.clone(),
         codex_home: config.codex_home.clone(),
         thread_name: None,
+        environment_selections: None,
         original_config_do_not_use: Arc::clone(&config),
         metrics_service_name: None,
         app_server_client_name: None,
@@ -3051,6 +3055,7 @@ async fn session_new_fails_when_zsh_fork_enabled_without_zsh_path() {
         cwd: config.cwd.clone(),
         codex_home: config.codex_home.clone(),
         thread_name: None,
+        environment_selections: None,
         original_config_do_not_use: Arc::clone(&config),
         metrics_service_name: None,
         app_server_client_name: None,
@@ -3151,6 +3156,7 @@ pub(crate) async fn make_session_and_context() -> (Session, TurnContext) {
         cwd: config.cwd.clone(),
         codex_home: config.codex_home.clone(),
         thread_name: None,
+        environment_selections: None,
         original_config_do_not_use: Arc::clone(&config),
         metrics_service_name: None,
         app_server_client_name: None,
@@ -3371,6 +3377,7 @@ async fn make_session_with_config_and_rx(
         cwd: config.cwd.clone(),
         codex_home: config.codex_home.clone(),
         thread_name: None,
+        environment_selections: None,
         original_config_do_not_use: Arc::clone(&config),
         metrics_service_name: None,
         app_server_client_name: None,
@@ -3850,6 +3857,7 @@ fn op_kind_distinguishes_turn_ops() {
             service_tier: None,
             collaboration_mode: None,
             personality: None,
+            environments: None,
         }
         .kind(),
         "override_turn_context"
@@ -4381,6 +4389,7 @@ where
         cwd: config.cwd.clone(),
         codex_home: config.codex_home.clone(),
         thread_name: None,
+        environment_selections: None,
         original_config_do_not_use: Arc::clone(&config),
         metrics_service_name: None,
         app_server_client_name: None,
diff --git a/codex-rs/core/src/session/tests/guardian_tests.rs b/codex-rs/core/src/session/tests/guardian_tests.rs
index 5fb7fe3316..06c189993c 100644
--- a/codex-rs/core/src/session/tests/guardian_tests.rs
+++ b/codex-rs/core/src/session/tests/guardian_tests.rs
@@ -651,6 +651,7 @@ async fn guardian_subagent_does_not_inherit_parent_exec_policy_rules() {
         inherited_exec_policy: Some(Arc::new(parent_exec_policy)),
         user_shell_override: None,
         parent_trace: None,
+        environment_selections: None,
         analytics_events_client: None,
     })
     .await
diff --git a/codex-rs/core/src/session/turn_context.rs b/codex-rs/core/src/session/turn_context.rs
index 998f016c96..b44a416520 100644
--- a/codex-rs/core/src/session/turn_context.rs
+++ b/codex-rs/core/src/session/turn_context.rs
@@ -467,20 +467,6 @@ impl Session {
         updates: SessionSettingsUpdate,
         environment_selections: Option<Vec<TurnEnvironmentSelection>>,
     ) -> CodexResult<Arc<TurnContext>> {
-        let turn_environments = match self.resolve_turn_environments(environment_selections) {
-            Ok(turn_environments) => turn_environments,
-            Err(err) => {
-                self.send_event_raw(Event {
-                    id: sub_id.clone(),
-                    msg: EventMsg::Error(ErrorEvent {
-                        message: err.to_string(),
-                        codex_error_info: Some(CodexErrorInfo::BadRequest),
-                    }),
-                })
-                .await;
-                return Err(err);
-            }
-        };
         let update_result = {
             let mut state = self.state.lock().await;
             match state.session_configuration.clone().apply(&updates) {
@@ -524,6 +510,23 @@ impl Session {
                 return Err(CodexErr::InvalidRequest(message));
             }
         };
+        let effective_environment_selections =
+            environment_selections.or_else(|| session_configuration.environment_selections.clone());
+        let turn_environments =
+            match self.resolve_turn_environments(effective_environment_selections) {
+                Ok(turn_environments) => turn_environments,
+                Err(err) => {
+                    self.send_event_raw(Event {
+                        id: sub_id.clone(),
+                        msg: EventMsg::Error(ErrorEvent {
+                            message: err.to_string(),
+                            codex_error_info: Some(CodexErrorInfo::BadRequest),
+                        }),
+                    })
+                    .await;
+                    return Err(err);
+                }
+            };
 
         self.maybe_refresh_shell_snapshot_for_cwd(
             &previous_cwd,
diff --git a/codex-rs/core/src/thread_manager.rs b/codex-rs/core/src/thread_manager.rs
index 066bfe3165..8c74cd3506 100644
--- a/codex-rs/core/src/thread_manager.rs
+++ b/codex-rs/core/src/thread_manager.rs
@@ -501,6 +501,7 @@ impl ThreadManager {
             persist_extended_history,
             /*metrics_service_name*/ None,
             /*parent_trace*/ None,
+            /*environment_selections*/ None,
         ))
         .await
     }
@@ -513,6 +514,7 @@ impl ThreadManager {
         persist_extended_history: bool,
         metrics_service_name: Option<String>,
         parent_trace: Option<W3cTraceContext>,
+        environment_selections: Option<Vec<codex_protocol::protocol::TurnEnvironmentSelection>>,
     ) -> CodexResult<NewThread> {
         Box::pin(self.state.spawn_thread(
             config,
@@ -523,6 +525,7 @@ impl ThreadManager {
             persist_extended_history,
             metrics_service_name,
             parent_trace,
+            environment_selections,
             /*user_shell_override*/ None,
         ))
         .await
@@ -563,6 +566,7 @@ impl ThreadManager {
             persist_extended_history,
             /*metrics_service_name*/ None,
             parent_trace,
+            /*environment_selections*/ None,
             /*user_shell_override*/ None,
         ))
         .await
@@ -582,6 +586,7 @@ impl ThreadManager {
             /*persist_extended_history*/ false,
             /*metrics_service_name*/ None,
             /*parent_trace*/ None,
+            /*environment_selections*/ None,
             /*user_shell_override*/ Some(user_shell_override),
         ))
         .await
@@ -604,6 +609,7 @@ impl ThreadManager {
             /*persist_extended_history*/ false,
             /*metrics_service_name*/ None,
             /*parent_trace*/ None,
+            /*environment_selections*/ None,
             /*user_shell_override*/ Some(user_shell_override),
         ))
         .await
@@ -712,6 +718,7 @@ impl ThreadManager {
             persist_extended_history,
             /*metrics_service_name*/ None,
             parent_trace,
+            /*environment_selections*/ None,
             /*user_shell_override*/ None,
         ))
         .await
@@ -813,6 +820,7 @@ impl ThreadManagerState {
             inherited_shell_snapshot,
             inherited_exec_policy,
             /*parent_trace*/ None,
+            /*environment_selections*/ None,
             /*user_shell_override*/ None,
         ))
         .await
@@ -840,6 +848,7 @@ impl ThreadManagerState {
             inherited_shell_snapshot,
             inherited_exec_policy,
             /*parent_trace*/ None,
+            /*environment_selections*/ None,
             /*user_shell_override*/ None,
         ))
         .await
@@ -868,6 +877,7 @@ impl ThreadManagerState {
             inherited_shell_snapshot,
             inherited_exec_policy,
             /*parent_trace*/ None,
+            /*environment_selections*/ None,
             /*user_shell_override*/ None,
         ))
         .await
@@ -885,6 +895,7 @@ impl ThreadManagerState {
         persist_extended_history: bool,
         metrics_service_name: Option<String>,
         parent_trace: Option<W3cTraceContext>,
+        environment_selections: Option<Vec<codex_protocol::protocol::TurnEnvironmentSelection>>,
         user_shell_override: Option<crate::shell::Shell>,
     ) -> CodexResult<NewThread> {
         Box::pin(self.spawn_thread_with_source(
@@ -899,6 +910,7 @@ impl ThreadManagerState {
             /*inherited_shell_snapshot*/ None,
             /*inherited_exec_policy*/ None,
             parent_trace,
+            environment_selections,
             user_shell_override,
         ))
         .await
@@ -918,6 +930,7 @@ impl ThreadManagerState {
         inherited_shell_snapshot: Option<Arc<ShellSnapshot>>,
         inherited_exec_policy: Option<Arc<crate::exec_policy::ExecPolicyManager>>,
         parent_trace: Option<W3cTraceContext>,
+        environment_selections: Option<Vec<codex_protocol::protocol::TurnEnvironmentSelection>>,
         user_shell_override: Option<crate::shell::Shell>,
     ) -> CodexResult<NewThread> {
         let environment = self.environment_manager.default_environment();
@@ -955,6 +968,7 @@ impl ThreadManagerState {
             inherited_exec_policy,
             user_shell_override,
             parent_trace,
+            environment_selections,
             analytics_events_client: self.analytics_events_client.clone(),
         })
         .await?;
diff --git a/codex-rs/protocol/src/protocol.rs b/codex-rs/protocol/src/protocol.rs
index 615bc5bb8f..6fe8e37e38 100644
--- a/codex-rs/protocol/src/protocol.rs
+++ b/codex-rs/protocol/src/protocol.rs
@@ -567,6 +567,10 @@ pub enum Op {
         /// Updated personality preference.
         #[serde(skip_serializing_if = "Option::is_none")]
         personality: Option<Personality>,
+
+        /// Updated sticky environment selections for future turns.
+        #[serde(default, skip_serializing_if = "Option::is_none")]
+        environments: Option<Vec<TurnEnvironmentSelection>>,
     },
 
     /// Approve a command execution