fix(core): pin AuthType.GATEWAY to use Gemini 3.1 Pro/Flash Lite by default (#24375)

packages/core/src/config/config.test.ts

@@ -591,6 +591,55 @@ describe('Server Config (config.ts)', () => {
         expect(await config.getResolvedClassifierThreshold()).toBe(90);
       });
     });
+
+    describe('getGemini31LaunchedSync', () => {
+      it.each([AuthType.USE_GEMINI, AuthType.USE_VERTEX_AI, AuthType.GATEWAY])(
+        'should return true for %s',
+        async (authType) => {
+          const config = new Config(baseParams);
+          vi.mocked(createContentGeneratorConfig).mockResolvedValue({
+            authType,
+          });
+          await config.refreshAuth(authType);
+          expect(config.getGemini31LaunchedSync()).toBe(true);
+        },
+      );
+
+      it('should fallback to experiments for other auth types', async () => {
+        vi.mocked(getExperiments).mockResolvedValue({
+          experimentIds: [],
+          flags: {
+            [ExperimentFlags.GEMINI_3_1_PRO_LAUNCHED]: {
+              flagId: ExperimentFlags.GEMINI_3_1_PRO_LAUNCHED,
+              boolValue: true,
+            },
+          },
+        });
+
+        const config = new Config(baseParams);
+
+        vi.mocked(createContentGeneratorConfig).mockResolvedValue({
+          authType: AuthType.LOGIN_WITH_GOOGLE,
+        });
+
+        await config.refreshAuth(AuthType.LOGIN_WITH_GOOGLE);
+        expect(config.getGemini31LaunchedSync()).toBe(true);
+      });
+    });
+
+    describe('getGemini31FlashLiteLaunchedSync', () => {
+      it.each([AuthType.USE_GEMINI, AuthType.USE_VERTEX_AI, AuthType.GATEWAY])(
+        'should return true for %s',
+        async (authType) => {
+          const config = new Config(baseParams);
+          vi.mocked(createContentGeneratorConfig).mockResolvedValue({
+            authType,
+          });
+          await config.refreshAuth(authType);
+          expect(config.getGemini31FlashLiteLaunchedSync()).toBe(true);
+        },
+      );
+    });
   });
 
   describe('refreshAuth', () => {

packages/core/src/config/config.ts

@@ -3083,6 +3083,14 @@ export class Config implements McpContext, AgentLoopContext {
     return useGemini3_1 && authType === AuthType.USE_GEMINI;
   }
 
+  private isGemini31LaunchedForAuthType(authType?: AuthType): boolean {
+    return (
+      authType === AuthType.USE_GEMINI ||
+      authType === AuthType.USE_VERTEX_AI ||
+      authType === AuthType.GATEWAY
+    );
+  }
+
   /**
    * Returns whether Gemini 3.1 has been launched.
    *
@@ -3092,10 +3100,7 @@ export class Config implements McpContext, AgentLoopContext {
    */
   getGemini31LaunchedSync(): boolean {
     const authType = this.contentGeneratorConfig?.authType;
-    if (
+    if (this.isGemini31LaunchedForAuthType(authType)) {
-      authType === AuthType.USE_GEMINI ||
-      authType === AuthType.USE_VERTEX_AI
-    ) {
       return true;
     }
     return (
@@ -3113,10 +3118,7 @@ export class Config implements McpContext, AgentLoopContext {
    */
   getGemini31FlashLiteLaunchedSync(): boolean {
     const authType = this.contentGeneratorConfig?.authType;
-    if (
+    if (this.isGemini31LaunchedForAuthType(authType)) {
-      authType === AuthType.USE_GEMINI ||
-      authType === AuthType.USE_VERTEX_AI
-    ) {
       return true;
     }
     return (