diff --git a/cli/src/codex/loop.ts b/cli/src/codex/loop.ts
index d0d170c4..51a5c7aa 100644
--- a/cli/src/codex/loop.ts
+++ b/cli/src/codex/loop.ts
@@ -7,12 +7,14 @@ import { codexRemoteLauncher } from './codexRemoteLauncher';
 import { ApiClient, ApiSessionClient } from '@/lib';
 import type { CodexCliOverrides } from './utils/codexCliOverrides';
 import type { CodexPermissionMode } from '@hapi/protocol/types';
+import type { CollaborationMode } from './appServerTypes';
 
 export type PermissionMode = CodexPermissionMode;
 
 export interface EnhancedMode {
     permissionMode: PermissionMode;
     model?: string;
+    collaborationMode?: CollaborationMode['mode'];
 }
 
 interface LoopOptions {
diff --git a/cli/src/codex/runCodex.ts b/cli/src/codex/runCodex.ts
index 16768d55..91657eca 100644
--- a/cli/src/codex/runCodex.ts
+++ b/cli/src/codex/runCodex.ts
@@ -42,7 +42,8 @@ export async function runCodex(opts: {
 
     const messageQueue = new MessageQueue2<EnhancedMode>((mode) => hashObject({
         permissionMode: mode.permissionMode,
-        model: mode.model
+        model: mode.model,
+        collaborationMode: mode.collaborationMode
     }));
 
     const codexCliOverrides = parseCodexCliOverrides(opts.codexArgs);
@@ -50,6 +51,7 @@ export async function runCodex(opts: {
 
     let currentPermissionMode: PermissionMode = opts.permissionMode ?? 'default';
     const currentModel = opts.model;
+    let currentCollaborationMode: EnhancedMode['collaborationMode'];
 
     const lifecycle = createRunnerLifecycle({
         session,
@@ -75,7 +77,8 @@ export async function runCodex(opts: {
 
         const enhancedMode: EnhancedMode = {
             permissionMode: messagePermissionMode ?? 'default',
-            model: currentModel
+            model: currentModel,
+            collaborationMode: currentCollaborationMode
         };
         const formattedText = formatMessageWithAttachments(message.content.text, message.content.attachments);
         messageQueue.push(formattedText, enhancedMode);
@@ -97,18 +100,36 @@ export async function runCodex(opts: {
         return parsed.data as PermissionMode;
     };
 
+    const resolveCollaborationMode = (value: unknown): EnhancedMode['collaborationMode'] => {
+        if (value === null) {
+            return undefined;
+        }
+        if (typeof value !== 'string') {
+            throw new Error('Invalid collaboration mode');
+        }
+        const trimmed = value.trim();
+        if (!trimmed) {
+            throw new Error('Invalid collaboration mode');
+        }
+        return trimmed as EnhancedMode['collaborationMode'];
+    };
+
     session.rpcHandlerManager.registerHandler('set-session-config', async (payload: unknown) => {
         if (!payload || typeof payload !== 'object') {
             throw new Error('Invalid session config payload');
         }
-        const config = payload as { permissionMode?: unknown };
+        const config = payload as { permissionMode?: unknown; collaborationMode?: unknown };
 
         if (config.permissionMode !== undefined) {
             currentPermissionMode = resolvePermissionMode(config.permissionMode);
         }
 
+        if (config.collaborationMode !== undefined) {
+            currentCollaborationMode = resolveCollaborationMode(config.collaborationMode);
+        }
+
         syncSessionMode();
-        return { applied: { permissionMode: currentPermissionMode } };
+        return { applied: { permissionMode: currentPermissionMode, collaborationMode: currentCollaborationMode } };
     });
 
     try {
diff --git a/cli/src/codex/utils/appServerConfig.test.ts b/cli/src/codex/utils/appServerConfig.test.ts
index 2cc03759..1155b7bd 100644
--- a/cli/src/codex/utils/appServerConfig.test.ts
+++ b/cli/src/codex/utils/appServerConfig.test.ts
@@ -48,6 +48,17 @@ describe('appServerConfig', () => {
         expect(params.model).toBe('o3');
     });
 
+    it('puts collaboration mode in turn params with model settings', () => {
+        const params = buildTurnStartParams({
+            threadId: 'thread-1',
+            message: 'hello',
+            mode: { permissionMode: 'default', model: 'o3', collaborationMode: 'plan' }
+        });
+
+        expect(params.collaborationMode).toEqual({ mode: 'plan', settings: { model: 'o3' } });
+        expect(params.model).toBeUndefined();
+    });
+
     it('applies CLI overrides for turns when permission mode is default', () => {
         const params = buildTurnStartParams({
             threadId: 'thread-1',
diff --git a/cli/src/codex/utils/appServerConfig.ts b/cli/src/codex/utils/appServerConfig.ts
index f9abb67f..5a2aa102 100644
--- a/cli/src/codex/utils/appServerConfig.ts
+++ b/cli/src/codex/utils/appServerConfig.ts
@@ -136,8 +136,14 @@ export function buildTurnStartParams(args: {
         params.sandboxPolicy = sandboxPolicy;
     }
 
+    const collaborationMode = args.mode?.collaborationMode;
     const model = args.overrides?.model ?? args.mode?.model;
-    if (model) {
+    if (collaborationMode) {
+        const settings = model ? { model } : undefined;
+        params.collaborationMode = settings
+            ? { mode: collaborationMode, settings }
+            : { mode: collaborationMode };
+    } else if (model) {
         params.model = model;
     }