diff --git a/codex-rs/codex-api/src/requests/chat.rs b/codex-rs/codex-api/src/requests/chat.rs
index 60a591e5c2..13408fe20d 100644
--- a/codex-rs/codex-api/src/requests/chat.rs
+++ b/codex-rs/codex-api/src/requests/chat.rs
@@ -69,7 +69,9 @@ impl<'a> ChatRequestBuilder<'a> {
                     last_emitted_role = Some("assistant")
                 }
                 ResponseItem::FunctionCallOutput { .. } => last_emitted_role = Some("tool"),
-                ResponseItem::Reasoning { .. } | ResponseItem::Other => {}
+                ResponseItem::Reasoning { .. }
+                | ResponseItem::CollaborationModeUpdate { .. }
+                | ResponseItem::Other => {}
                 ResponseItem::CustomToolCall { .. } => {}
                 ResponseItem::CustomToolCallOutput { .. } => {}
                 ResponseItem::WebSearchCall { .. } => {}
@@ -284,6 +286,7 @@ impl<'a> ChatRequestBuilder<'a> {
                 }
                 ResponseItem::Reasoning { .. }
                 | ResponseItem::WebSearchCall { .. }
+                | ResponseItem::CollaborationModeUpdate { .. }
                 | ResponseItem::Other
                 | ResponseItem::Compaction { .. } => {
                     continue;
diff --git a/codex-rs/core/src/codex.rs b/codex-rs/core/src/codex.rs
index 2744fd7f35..0279fa8502 100644
--- a/codex-rs/core/src/codex.rs
+++ b/codex-rs/core/src/codex.rs
@@ -42,7 +42,6 @@ use async_channel::Receiver;
 use async_channel::Sender;
 use codex_protocol::ThreadId;
 use codex_protocol::approvals::ExecPolicyAmendment;
-use codex_protocol::config_types::ModeKind;
 use codex_protocol::config_types::Settings;
 use codex_protocol::config_types::WebSearchMode;
 use codex_protocol::dynamic_tools::DynamicToolResponse;
@@ -206,6 +205,8 @@ use crate::windows_sandbox::WindowsSandboxLevelExt;
 use codex_async_utils::OrCancelExt;
 use codex_otel::OtelManager;
 use codex_protocol::config_types::CollaborationMode;
+use codex_protocol::config_types::CollaborationModeMask;
+use codex_protocol::config_types::ModeKind;
 use codex_protocol::config_types::Personality;
 use codex_protocol::config_types::ReasoningSummary as ReasoningSummaryConfig;
 use codex_protocol::config_types::WindowsSandboxLevel;
@@ -1400,6 +1401,26 @@ impl Session {
         }
     }
 
+    fn collaboration_mode_mask_from_mode(mode: &CollaborationMode) -> CollaborationModeMask {
+        CollaborationModeMask {
+            name: Self::collaboration_mode_name(mode.mode).to_string(),
+            mode: Some(mode.mode),
+            model: Some(mode.model().to_string()),
+            reasoning_effort: Some(mode.reasoning_effort()),
+            developer_instructions: Some(mode.settings.developer_instructions.clone()),
+        }
+    }
+
+    fn collaboration_mode_name(kind: ModeKind) -> &'static str {
+        match kind {
+            ModeKind::Plan => "Plan",
+            ModeKind::Code => "Code",
+            ModeKind::PairProgramming => "Pair Programming",
+            ModeKind::Execute => "Execute",
+            ModeKind::Custom => "Custom",
+        }
+    }
+
     fn build_settings_update_items(
         &self,
         previous_context: Option<&Arc<TurnContext>>,
@@ -1416,9 +1437,17 @@ impl Session {
         {
             update_items.push(permissions_item);
         }
-        if let Some(collaboration_mode_item) =
-            self.build_collaboration_mode_update_item(previous_context, current_context)
-        {
+        if let Some(next_mode) = next_collaboration_mode {
+            if previous_collaboration_mode != next_mode {
+                update_items.push(ResponseItem::CollaborationModeUpdate {
+                    mask: Self::collaboration_mode_mask_from_mode(next_mode),
+                });
+            }
+        }
+        if let Some(collaboration_mode_item) = self.build_collaboration_mode_update_item(
+            previous_collaboration_mode,
+            next_collaboration_mode,
+        ) {
             update_items.push(collaboration_mode_item);
         }
         if let Some(personality_item) =
@@ -1924,6 +1953,9 @@ impl Session {
                 state.session_configuration.base_instructions.clone(),
             )
         };
+        items.push(ResponseItem::CollaborationModeUpdate {
+            mask: Self::collaboration_mode_mask_from_mode(&collaboration_mode),
+        });
         if let Some(collab_instructions) =
             DeveloperInstructions::from_collaboration_mode(&collaboration_mode)
         {
@@ -3117,6 +3149,9 @@ mod handlers {
 
     fn last_collaboration_mask(items: &[ResponseItem]) -> Option<CollaborationModeMask> {
         items.iter().rev().find_map(|item| {
+            if let ResponseItem::CollaborationModeUpdate { mask } = item {
+                return Some(mask.clone());
+            }
             let ResponseItem::Message { role, content, .. } = item else {
                 return None;
             };
diff --git a/codex-rs/core/src/context_manager/history.rs b/codex-rs/core/src/context_manager/history.rs
index a29f7df7e0..1ee297bcf2 100644
--- a/codex-rs/core/src/context_manager/history.rs
+++ b/codex-rs/core/src/context_manager/history.rs
@@ -59,7 +59,9 @@ impl ContextManager {
         for item in items {
             let item_ref = item.deref();
             let is_ghost_snapshot = matches!(item_ref, ResponseItem::GhostSnapshot { .. });
-            if !is_api_message(item_ref) && !is_ghost_snapshot {
+            let is_collaboration_mode_update =
+                matches!(item_ref, ResponseItem::CollaborationModeUpdate { .. });
+            if !is_api_message(item_ref) && !is_ghost_snapshot && !is_collaboration_mode_update {
                 continue;
             }
 
@@ -72,8 +74,12 @@ impl ContextManager {
     /// normalization and drop un-suited items.
     pub(crate) fn for_prompt(mut self) -> Vec<ResponseItem> {
         self.normalize_history();
-        self.items
-            .retain(|item| !matches!(item, ResponseItem::GhostSnapshot { .. }));
+        self.items.retain(|item| {
+            !matches!(
+                item,
+                ResponseItem::GhostSnapshot { .. } | ResponseItem::CollaborationModeUpdate { .. }
+            )
+        });
         self.items
     }
 
@@ -302,6 +308,7 @@ impl ContextManager {
             | ResponseItem::CustomToolCall { .. }
             | ResponseItem::Compaction { .. }
             | ResponseItem::GhostSnapshot { .. }
+            | ResponseItem::CollaborationModeUpdate { .. }
             | ResponseItem::Other => item.clone(),
         }
     }
@@ -321,6 +328,7 @@ fn is_api_message(message: &ResponseItem) -> bool {
         | ResponseItem::WebSearchCall { .. }
         | ResponseItem::Compaction { .. } => true,
         ResponseItem::GhostSnapshot { .. } => false,
+        ResponseItem::CollaborationModeUpdate { .. } => false,
         ResponseItem::Other => false,
     }
 }
@@ -335,7 +343,7 @@ fn estimate_reasoning_length(encoded_len: usize) -> usize {
 
 fn estimate_item_token_count(item: &ResponseItem) -> i64 {
     match item {
-        ResponseItem::GhostSnapshot { .. } => 0,
+        ResponseItem::GhostSnapshot { .. } | ResponseItem::CollaborationModeUpdate { .. } => 0,
         ResponseItem::Reasoning {
             encrypted_content: Some(content),
             ..
diff --git a/codex-rs/core/src/rollout/policy.rs b/codex-rs/core/src/rollout/policy.rs
index 5796bd1961..31b9cbcb61 100644
--- a/codex-rs/core/src/rollout/policy.rs
+++ b/codex-rs/core/src/rollout/policy.rs
@@ -27,6 +27,7 @@ pub(crate) fn should_persist_response_item(item: &ResponseItem) -> bool {
         | ResponseItem::CustomToolCall { .. }
         | ResponseItem::CustomToolCallOutput { .. }
         | ResponseItem::WebSearchCall { .. }
+        | ResponseItem::CollaborationModeUpdate { .. }
         | ResponseItem::GhostSnapshot { .. }
         | ResponseItem::Compaction { .. } => true,
         ResponseItem::Other => false,
diff --git a/codex-rs/otel/src/traces/otel_manager.rs b/codex-rs/otel/src/traces/otel_manager.rs
index c585ec67d5..445831adac 100644
--- a/codex-rs/otel/src/traces/otel_manager.rs
+++ b/codex-rs/otel/src/traces/otel_manager.rs
@@ -679,6 +679,7 @@ impl OtelManager {
             ResponseItem::CustomToolCall { .. } => "custom_tool_call".into(),
             ResponseItem::CustomToolCallOutput { .. } => "custom_tool_call_output".into(),
             ResponseItem::WebSearchCall { .. } => "web_search_call".into(),
+            ResponseItem::CollaborationModeUpdate { .. } => "collaboration_mode_update".into(),
             ResponseItem::GhostSnapshot { .. } => "ghost_snapshot".into(),
             ResponseItem::Compaction { .. } => "compaction".into(),
             ResponseItem::Other => "other".into(),
diff --git a/codex-rs/protocol/src/models.rs b/codex-rs/protocol/src/models.rs
index 74cc9a53f1..bbae6f9af2 100644
--- a/codex-rs/protocol/src/models.rs
+++ b/codex-rs/protocol/src/models.rs
@@ -9,6 +9,7 @@ use serde::ser::Serializer;
 use ts_rs::TS;
 
 use crate::config_types::CollaborationMode;
+use crate::config_types::CollaborationModeMask;
 use crate::config_types::SandboxMode;
 use crate::protocol::AskForApproval;
 use crate::protocol::COLLABORATION_MODE_CLOSE_TAG;
@@ -98,6 +99,9 @@ pub enum ResponseItem {
         #[ts(optional)]
         phase: Option<MessagePhase>,
     },
+    CollaborationModeUpdate {
+        mask: CollaborationModeMask,
+    },
     Reasoning {
         #[serde(default, skip_serializing)]
         #[ts(skip)]