From 0e7b3951c253f514a46662826839057e0a8caa2e Mon Sep 17 00:00:00 2001
From: Victor May <mayvic@google.com>
Date: Tue, 21 Oct 2025 09:25:51 -0400
Subject: [PATCH] Per-Auth Method Feature Flag for Model Routing (#11333)

Co-authored-by: Abhi <43648792+abhipatel12@users.noreply.github.com>
---
 packages/cli/src/config/config.test.ts  |  1 +
 packages/core/src/config/config.test.ts | 47 +++++++++++++++++++------
 packages/core/src/config/config.ts      | 22 ++++++++++--
 3 files changed, 57 insertions(+), 13 deletions(-)

diff --git a/packages/cli/src/config/config.test.ts b/packages/cli/src/config/config.test.ts
index 6bc23ad7d6..1a8dab99e9 100644
--- a/packages/cli/src/config/config.test.ts
+++ b/packages/cli/src/config/config.test.ts
@@ -85,6 +85,7 @@ vi.mock('@google/gemini-cli-core', async () => {
   const actualServer = await vi.importActual<typeof ServerConfig>(
     '@google/gemini-cli-core',
   );
+
   return {
     ...actualServer,
     IdeClient: {
diff --git a/packages/core/src/config/config.test.ts b/packages/core/src/config/config.test.ts
index 0546f7cba6..b5e99a5e37 100644
--- a/packages/core/src/config/config.test.ts
+++ b/packages/core/src/config/config.test.ts
@@ -574,27 +574,52 @@ describe('Server Config (config.ts)', () => {
     });
   });
 
-  describe('UseModelRouter Configuration', () => {
-    it('should default useModelRouter to false when not provided', () => {
-      const config = new Config(baseParams);
+  describe('Model Router with Auth', () => {
+    it('should disable model router by default for oauth-personal', async () => {
+      const config = new Config({
+        ...baseParams,
+        useModelRouter: true,
+      });
+      await config.refreshAuth(AuthType.LOGIN_WITH_GOOGLE);
       expect(config.getUseModelRouter()).toBe(false);
     });
 
-    it('should set useModelRouter to true when provided as true', () => {
-      const paramsWithModelRouter: ConfigParameters = {
+    it('should enable model router by default for other auth types', async () => {
+      const config = new Config({
         ...baseParams,
         useModelRouter: true,
-      };
-      const config = new Config(paramsWithModelRouter);
+      });
+      await config.refreshAuth(AuthType.USE_GEMINI);
       expect(config.getUseModelRouter()).toBe(true);
     });
 
-    it('should set useModelRouter to false when explicitly provided as false', () => {
-      const paramsWithModelRouter: ConfigParameters = {
+    it('should disable model router for specified auth type', async () => {
+      const config = new Config({
+        ...baseParams,
+        useModelRouter: true,
+        disableModelRouterForAuth: [AuthType.USE_GEMINI],
+      });
+      await config.refreshAuth(AuthType.USE_GEMINI);
+      expect(config.getUseModelRouter()).toBe(false);
+    });
+
+    it('should enable model router for other auth type', async () => {
+      const config = new Config({
+        ...baseParams,
+        useModelRouter: true,
+        disableModelRouterForAuth: [],
+      });
+      await config.refreshAuth(AuthType.LOGIN_WITH_GOOGLE);
+      expect(config.getUseModelRouter()).toBe(true);
+    });
+
+    it('should keep model router disabled when useModelRouter is false', async () => {
+      const config = new Config({
         ...baseParams,
         useModelRouter: false,
-      };
-      const config = new Config(paramsWithModelRouter);
+        disableModelRouterForAuth: [AuthType.USE_GEMINI],
+      });
+      await config.refreshAuth(AuthType.LOGIN_WITH_GOOGLE);
       expect(config.getUseModelRouter()).toBe(false);
     });
   });
diff --git a/packages/core/src/config/config.ts b/packages/core/src/config/config.ts
index 584e928cb0..4955a0f95e 100644
--- a/packages/core/src/config/config.ts
+++ b/packages/core/src/config/config.ts
@@ -47,6 +47,7 @@ import {
   DEFAULT_GEMINI_EMBEDDING_MODEL,
   DEFAULT_GEMINI_FLASH_MODEL,
   DEFAULT_GEMINI_MODEL,
+  DEFAULT_GEMINI_MODEL_AUTO,
   DEFAULT_THINKING_MODE,
 } from './models.js';
 import { shouldAttemptBrowserLaunch } from '../utils/browser.js';
@@ -278,6 +279,7 @@ export interface ConfigParameters {
   policyEngineConfig?: PolicyEngineConfig;
   output?: OutputSettings;
   useModelRouter?: boolean;
+  disableModelRouterForAuth?: AuthType[];
   enableMessageBusIntegration?: boolean;
   codebaseInvestigatorSettings?: CodebaseInvestigatorSettings;
   continueOnFailedApiCall?: boolean;
@@ -374,7 +376,9 @@ export class Config {
   private readonly messageBus: MessageBus;
   private readonly policyEngine: PolicyEngine;
   private readonly outputSettings: OutputSettings;
-  private readonly useModelRouter: boolean;
+  private useModelRouter: boolean;
+  private readonly initialUseModelRouter: boolean;
+  private readonly disableModelRouterForAuth?: AuthType[];
   private readonly enableMessageBusIntegration: boolean;
   private readonly codebaseInvestigatorSettings: CodebaseInvestigatorSettings;
   private readonly continueOnFailedApiCall: boolean;
@@ -470,7 +474,11 @@ export class Config {
     this.enableToolOutputTruncation = params.enableToolOutputTruncation ?? true;
     this.useSmartEdit = params.useSmartEdit ?? true;
     this.useWriteTodos = params.useWriteTodos ?? false;
-    this.useModelRouter = params.useModelRouter ?? false;
+    this.initialUseModelRouter = params.useModelRouter ?? false;
+    this.useModelRouter = this.initialUseModelRouter;
+    this.disableModelRouterForAuth = params.disableModelRouterForAuth ?? [
+      AuthType.LOGIN_WITH_GOOGLE,
+    ];
     this.enableMessageBusIntegration =
       params.enableMessageBusIntegration ?? false;
     this.codebaseInvestigatorSettings = {
@@ -541,6 +549,16 @@ export class Config {
   }
 
   async refreshAuth(authMethod: AuthType) {
+    this.useModelRouter = this.initialUseModelRouter;
+    if (this.disableModelRouterForAuth?.includes(authMethod)) {
+      this.useModelRouter = false;
+      if (this.model === DEFAULT_GEMINI_MODEL_AUTO) {
+        this.model = DEFAULT_GEMINI_MODEL;
+      }
+    } else {
+      this.model = DEFAULT_GEMINI_MODEL_AUTO;
+    }
+
     // Vertex and Genai have incompatible encryption and sending history with
     // thoughtSignature from Genai to Vertex will fail, we need to strip them
     if (