feat(core,ui): Add experiment-gated support for gemini flash 3.1 lite (#23794)

Author: chrstnb

docs/reference/configuration.md

@@ -645,6 +645,11 @@ their corresponding top-level category object in your `settings.json` file.
           "model": "gemini-3-flash-preview"
         }
       },
+      "chat-compression-3.1-flash-lite": {
+        "modelConfig": {
+          "model": "gemini-3.1-flash-lite-preview"
+        }
+      },
       "chat-compression-2.5-pro": {
         "modelConfig": {
           "model": "gemini-2.5-pro"
@@ -973,6 +978,17 @@ their corresponding top-level category object in your `settings.json` file.
       "auto-gemini-2.5": {
         "default": "gemini-2.5-pro"
       },
+      "gemini-3.1-flash-lite-preview": {
+        "default": "gemini-3.1-flash-lite-preview",
+        "contexts": [
+          {
+            "condition": {
+              "useGemini3_1FlashLite": false
+            },
+            "target": "gemini-2.5-flash-lite"
+          }
+        ]
+      },
       "flash": {
         "default": "gemini-3-flash-preview",
         "contexts": [
@@ -985,7 +1001,15 @@ their corresponding top-level category object in your `settings.json` file.
         ]
       },
       "flash-lite": {
-        "default": "gemini-2.5-flash-lite"
+        "default": "gemini-2.5-flash-lite",
+        "contexts": [
+          {
+            "condition": {
+              "useGemini3_1FlashLite": true
+            },
+            "target": "gemini-3.1-flash-lite-preview"
+          }
+        ]
       }
     }
     ```

packages/cli/src/config/settingsSchema.ts

@@ -3014,6 +3014,7 @@ export const SETTINGS_SCHEMA_DEFINITIONS: Record<
               type: 'object',
               properties: {
                 useGemini3_1: { type: 'boolean' },
+                useGemini3_1FlashLite: { type: 'boolean' },
                 useCustomTools: { type: 'boolean' },
                 hasAccessToPreview: { type: 'boolean' },
                 requestedModels: {

packages/cli/src/ui/components/ModelDialog.test.tsx

@@ -53,6 +53,7 @@ describe('<ModelDialog />', () => {
   const mockOnClose = vi.fn();
   const mockGetHasAccessToPreviewModel = vi.fn();
   const mockGetGemini31LaunchedSync = vi.fn();
+  const mockGetGemini31FlashLiteLaunchedSync = vi.fn();
   const mockGetProModelNoAccess = vi.fn();
   const mockGetProModelNoAccessSync = vi.fn();
   const mockGetUserTier = vi.fn();
@@ -63,6 +64,7 @@ describe('<ModelDialog />', () => {
     getHasAccessToPreviewModel: () => boolean;
     getIdeMode: () => boolean;
     getGemini31LaunchedSync: () => boolean;
+    getGemini31FlashLiteLaunchedSync: () => boolean;
     getProModelNoAccess: () => Promise<boolean>;
     getProModelNoAccessSync: () => boolean;
     getUserTier: () => UserTierId | undefined;
@@ -74,6 +76,7 @@ describe('<ModelDialog />', () => {
     getHasAccessToPreviewModel: mockGetHasAccessToPreviewModel,
     getIdeMode: () => false,
     getGemini31LaunchedSync: mockGetGemini31LaunchedSync,
+    getGemini31FlashLiteLaunchedSync: mockGetGemini31FlashLiteLaunchedSync,
     getProModelNoAccess: mockGetProModelNoAccess,
     getProModelNoAccessSync: mockGetProModelNoAccessSync,
     getUserTier: mockGetUserTier,
@@ -84,6 +87,7 @@ describe('<ModelDialog />', () => {
     mockGetModel.mockReturnValue(DEFAULT_GEMINI_MODEL_AUTO);
     mockGetHasAccessToPreviewModel.mockReturnValue(false);
     mockGetGemini31LaunchedSync.mockReturnValue(false);
+    mockGetGemini31FlashLiteLaunchedSync.mockReturnValue(false);
     mockGetProModelNoAccess.mockResolvedValue(false);
     mockGetProModelNoAccessSync.mockReturnValue(false);
     mockGetUserTier.mockReturnValue(UserTierId.STANDARD);
@@ -131,6 +135,7 @@ describe('<ModelDialog />', () => {
     mockGetProModelNoAccessSync.mockReturnValue(true);
     mockGetProModelNoAccess.mockResolvedValue(true);
     mockGetHasAccessToPreviewModel.mockReturnValue(true);
+    mockGetGemini31FlashLiteLaunchedSync.mockReturnValue(true);
     mockGetUserTier.mockReturnValue(UserTierId.FREE);
     mockGetDisplayString.mockImplementation((val: string) => val);
 
@@ -463,6 +468,7 @@ describe('<ModelDialog />', () => {
       mockGetProModelNoAccessSync.mockReturnValue(false);
       mockGetProModelNoAccess.mockResolvedValue(false);
       mockGetHasAccessToPreviewModel.mockReturnValue(true);
+      mockGetGemini31FlashLiteLaunchedSync.mockReturnValue(true);
       mockGetUserTier.mockReturnValue(UserTierId.FREE);
       const { lastFrame, stdin, waitUntilReady, unmount } =
         await renderComponent();

packages/cli/src/ui/components/ModelDialog.tsx

@@ -63,6 +63,8 @@ export function ModelDialog({ onClose }: ModelDialogProps): React.JSX.Element {
 
   const shouldShowPreviewModels = config?.getHasAccessToPreviewModel();
   const useGemini31 = config?.getGemini31LaunchedSync?.() ?? false;
+  const useGemini31FlashLite =
+    config?.getGemini31FlashLiteLaunchedSync?.() ?? false;
   const selectedAuthType = settings.merged.security.auth.selectedType;
   const useCustomToolModel =
     useGemini31 && selectedAuthType === AuthType.USE_GEMINI;
@@ -86,6 +88,7 @@ export function ModelDialog({ onClose }: ModelDialogProps): React.JSX.Element {
       PREVIEW_GEMINI_MODEL,
       PREVIEW_GEMINI_3_1_MODEL,
       PREVIEW_GEMINI_3_1_CUSTOM_TOOLS_MODEL,
+      PREVIEW_GEMINI_3_1_FLASH_LITE_MODEL,
       PREVIEW_GEMINI_FLASH_MODEL,
     ];
     if (manualModels.includes(preferredModel)) {
@@ -210,19 +213,24 @@ export function ModelDialog({ onClose }: ModelDialogProps): React.JSX.Element {
 
           // Flag Guard: Versioned models only show if their flag is active.
           if (id === PREVIEW_GEMINI_3_1_MODEL && !useGemini31) return false;
-          if (id === PREVIEW_GEMINI_3_1_FLASH_LITE_MODEL && !useGemini31)
+          if (
+            id === PREVIEW_GEMINI_3_1_FLASH_LITE_MODEL &&
+            !useGemini31FlashLite
+          )
             return false;
 
           return true;
         })
         .map(([id, m]) => {
           const resolvedId = config.modelConfigService.resolveModelId(id, {
             useGemini3_1: useGemini31,
+            useGemini3_1FlashLite: useGemini31FlashLite,
             useCustomTools: useCustomToolModel,
           });
           // Title ID is the resolved ID without custom tools flag
           const titleId = config.modelConfigService.resolveModelId(id, {
             useGemini3_1: useGemini31,
+            useGemini3_1FlashLite: useGemini31FlashLite,
           });
           return {
             value: resolvedId,
@@ -284,7 +292,7 @@ export function ModelDialog({ onClose }: ModelDialogProps): React.JSX.Element {
         },
       ];
 
-      if (isFreeTier) {
+      if (isFreeTier && useGemini31FlashLite) {
         previewOptions.push({
           value: PREVIEW_GEMINI_3_1_FLASH_LITE_MODEL,
           title: getDisplayString(PREVIEW_GEMINI_3_1_FLASH_LITE_MODEL),
@@ -304,6 +312,7 @@ export function ModelDialog({ onClose }: ModelDialogProps): React.JSX.Element {
   }, [
     shouldShowPreviewModels,
     useGemini31,
+    useGemini31FlashLite,
     useCustomToolModel,
     hasAccessToProModel,
     config,

packages/cli/src/ui/components/StatsDisplay.tsx

@@ -92,6 +92,7 @@ const buildModelRows = (
   config: Config,
   quotas?: RetrieveUserQuotaResponse,
   useGemini3_1 = false,
+  useGemini3_1FlashLite = false,
   useCustomToolModel = false,
 ) => {
   const getBaseModelName = (name: string) => name.replace('-001', '');
@@ -124,7 +125,12 @@ const buildModelRows = (
       ?.filter(
         (b) =>
           b.modelId &&
-          isActiveModel(b.modelId, useGemini3_1, useCustomToolModel) &&
+          isActiveModel(
+            b.modelId,
+            useGemini3_1,
+            useGemini3_1FlashLite,
+            useCustomToolModel,
+          ) &&
           !usedModelNames.has(getDisplayString(b.modelId, config)),
       )
       .map((bucket) => ({
@@ -152,6 +158,7 @@ const ModelUsageTable: React.FC<{
   pooledLimit?: number;
   pooledResetTime?: string;
   useGemini3_1?: boolean;
+  useGemini3_1FlashLite?: boolean;
   useCustomToolModel?: boolean;
 }> = ({
   models,
@@ -164,6 +171,7 @@ const ModelUsageTable: React.FC<{
   pooledLimit,
   pooledResetTime,
   useGemini3_1,
+  useGemini3_1FlashLite,
   useCustomToolModel,
 }) => {
   const { stdout } = useStdout();
@@ -173,6 +181,7 @@ const ModelUsageTable: React.FC<{
     config,
     quotas,
     useGemini3_1,
+    useGemini3_1FlashLite,
     useCustomToolModel,
   );
 
@@ -541,6 +550,8 @@ export const StatsDisplay: React.FC<StatsDisplayProps> = ({
   const settings = useSettings();
   const config = useConfig();
   const useGemini3_1 = config.getGemini31LaunchedSync?.() ?? false;
+  const useGemini3_1FlashLite =
+    config.getGemini31FlashLiteLaunchedSync?.() ?? false;
   const useCustomToolModel =
     useGemini3_1 &&
     config.getContentGeneratorConfig().authType === AuthType.USE_GEMINI;
@@ -697,6 +708,7 @@ export const StatsDisplay: React.FC<StatsDisplayProps> = ({
         pooledLimit={pooledLimit}
         pooledResetTime={pooledResetTime}
         useGemini3_1={useGemini3_1}
+        useGemini3_1FlashLite={useGemini3_1FlashLite}
         useCustomToolModel={useCustomToolModel}
       />
       {renderFooter()}

packages/core/src/availability/policyCatalog.test.ts

@@ -28,6 +28,7 @@ describe('policyCatalog', () => {
     const chain = getModelPolicyChain({
       previewEnabled: true,
       useGemini31: true,
+      useGemini31FlashLite: false,
     });
     expect(chain[0]?.model).toBe(PREVIEW_GEMINI_3_1_MODEL);
     expect(chain).toHaveLength(2);
@@ -38,6 +39,7 @@ describe('policyCatalog', () => {
     const chain = getModelPolicyChain({
       previewEnabled: true,
       useGemini31: true,
+      useGemini31FlashLite: false,
       useCustomToolModel: true,
     });
     expect(chain[0]?.model).toBe(PREVIEW_GEMINI_3_1_CUSTOM_TOOLS_MODEL);

packages/core/src/availability/policyCatalog.ts

@@ -30,6 +30,7 @@ export interface ModelPolicyOptions {
   previewEnabled: boolean;
   userTier?: UserTierId;
   useGemini31?: boolean;
+  useGemini31FlashLite?: boolean;
   useCustomToolModel?: boolean;
 }
 
@@ -85,6 +86,7 @@ export function getModelPolicyChain(
     const previewModel = resolveModel(
       PREVIEW_GEMINI_MODEL,
       options.useGemini31,
+      options.useGemini31FlashLite,
       options.useCustomToolModel,
     );
     return [

packages/core/src/availability/policyHelpers.test.ts

@@ -27,6 +27,7 @@ const createMockConfig = (overrides: Partial<Config> = {}): Config => {
     getUserTier: () => undefined,
     getModel: () => 'gemini-2.5-pro',
     getGemini31LaunchedSync: () => false,
+    getGemini31FlashLiteLaunchedSync: () => false,
     getUseCustomToolModelSync: () => {
       const useGemini31 = config.getGemini31LaunchedSync();
       const authType = config.getContentGeneratorConfig().authType;
@@ -203,6 +204,7 @@ describe('policyHelpers', () => {
               getExperimentalDynamicModelConfiguration: () => dynamic,
               getModel: () => model,
               getGemini31LaunchedSync: () => useGemini31 ?? false,
+              getGemini31FlashLiteLaunchedSync: () => false,
               getHasAccessToPreviewModel: () => hasAccess ?? true,
               getContentGeneratorConfig: () => ({ authType }),
               modelConfigService: new ModelConfigService(DEFAULT_MODEL_CONFIGS),

packages/core/src/availability/policyHelpers.ts

@@ -45,12 +45,15 @@ export function resolvePolicyChain(
 
   let chain;
   const useGemini31 = config.getGemini31LaunchedSync?.() ?? false;
+  const useGemini31FlashLite =
+    config.getGemini31FlashLiteLaunchedSync?.() ?? false;
   const useCustomToolModel = config.getUseCustomToolModelSync?.() ?? false;
   const hasAccessToPreview = config.getHasAccessToPreviewModel?.() ?? true;
 
   const resolvedModel = resolveModel(
     modelFromConfig,
     useGemini31,
+    useGemini31FlashLite,
     useCustomToolModel,
     hasAccessToPreview,
     config,
@@ -64,6 +67,7 @@ export function resolvePolicyChain(
   if (config.getExperimentalDynamicModelConfiguration?.() === true) {
     const context = {
       useGemini3_1: useGemini31,
+      useGemini3_1FlashLite: useGemini31FlashLite,
       useCustomTools: useCustomToolModel,
     };
 
@@ -120,6 +124,7 @@ export function resolvePolicyChain(
         previewEnabled,
         userTier: config.getUserTier(),
         useGemini31,
+        useGemini31FlashLite,
         useCustomToolModel,
       });
     } else {
@@ -129,6 +134,7 @@ export function resolvePolicyChain(
         previewEnabled: false,
         userTier: config.getUserTier(),
         useGemini31,
+        useGemini31FlashLite,
         useCustomToolModel,
       });
     }

packages/core/src/code_assist/experiments/flagNames.ts

@@ -18,6 +18,7 @@ export const ExperimentFlags = {
   MASKING_PROTECT_LATEST_TURN: 45758819,
   GEMINI_3_1_PRO_LAUNCHED: 45760185,
   PRO_MODEL_NO_ACCESS: 45768879,
+  GEMINI_3_1_FLASH_LITE_LAUNCHED: 45771641,
 } as const;
 
 export type ExperimentFlagName =