feat(config): enable Gemma 4 models by default via Gemini API (#26307)

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

@@ -3673,7 +3673,7 @@ describe('Config JIT Initialization', () => {
       expect(config.getExperimentalGemma()).toBe(false);
     });
 
-    it('should return false when experimentalGemma is not provided', () => {
+    it('should return true when experimentalGemma is not provided', () => {
       const params: ConfigParameters = {
         sessionId: 'test-session',
         targetDir: '/tmp/test',
@@ -3683,7 +3683,7 @@ describe('Config JIT Initialization', () => {
       };
 
       config = new Config(params);
-      expect(config.getExperimentalGemma()).toBe(false);
+      expect(config.getExperimentalGemma()).toBe(true);
     });
 
     it('should be independent of experimentalMemoryV2', () => {

packages/core/src/config/config.ts

@@ -1179,7 +1179,7 @@ export class Config implements McpContext, AgentLoopContext {
     this.experimentalJitContext = params.experimentalJitContext ?? true;
     this.experimentalMemoryV2 = params.experimentalMemoryV2 ?? true;
     this.experimentalAutoMemory = params.experimentalAutoMemory ?? false;
-    this.experimentalGemma = params.experimentalGemma ?? false;
+    this.experimentalGemma = params.experimentalGemma ?? true;
     this.experimentalContextManagementConfig =
       params.experimentalContextManagementConfig;
     this.memoryBoundaryMarkers = params.memoryBoundaryMarkers ?? ['.git'];

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

@@ -595,9 +595,9 @@ describe('isActiveModel', () => {
     expect(isActiveModel(DEFAULT_GEMINI_FLASH_MODEL)).toBe(true);
   });
 
-  it('should return true for Gemma 4 models only when experimentalGemma is true', () => {
-    expect(isActiveModel(GEMMA_4_31B_IT_MODEL)).toBe(false);
-    expect(isActiveModel(GEMMA_4_26B_A4B_IT_MODEL)).toBe(false);
+  it('should return true for Gemma 4 models when experimentalGemma is not provided (defaults to true)', () => {
+    expect(isActiveModel(GEMMA_4_31B_IT_MODEL)).toBe(true);
+    expect(isActiveModel(GEMMA_4_26B_A4B_IT_MODEL)).toBe(true);
     expect(isActiveModel(GEMMA_4_31B_IT_MODEL, false, false, false, true)).toBe(
       true,
     );

packages/core/src/config/models.ts

@@ -455,7 +455,7 @@ export function isActiveModel(
   useGemini3_1: boolean = false,
   useGemini3_1FlashLite: boolean = false,
   useCustomToolModel: boolean = false,
-  experimentalGemma: boolean = false,
+  experimentalGemma: boolean = true,
 ): boolean {
   if (!VALID_GEMINI_MODELS.has(model)) {
     return false;