Use Preview Flash model if the main model is a preview model for code… (#83)

* Use Preview Flash model if the main model is a preview model for codebase investigator

* fix test

* Generate settings doc

docs/get-started/configuration.md

@@ -832,7 +832,7 @@ their corresponding top-level category object in your `settings.json` file.
 
 - **`experimental.codebaseInvestigatorSettings.model`** (string):
   - **Description:** The model to use for the Codebase Investigator agent.
-  - **Default:** `"gemini-2.5-pro"`
+  - **Default:** `"auto"`
   - **Requires restart:** Yes
 
 #### `hooks`

packages/cli/src/config/settingsSchema.ts

@@ -19,7 +19,7 @@ import {
   DEFAULT_TRUNCATE_TOOL_OUTPUT_LINES,
   DEFAULT_TRUNCATE_TOOL_OUTPUT_THRESHOLD,
   DEFAULT_MODEL_CONFIGS,
-  DEFAULT_GEMINI_MODEL,
+  GEMINI_MODEL_ALIAS_AUTO,
 } from '@google/gemini-cli-core';
 import type { CustomTheme } from '../ui/themes/theme.js';
 import type { SessionRetentionSettings } from './settings.js';
@@ -1394,7 +1394,7 @@ const SETTINGS_SCHEMA = {
             label: 'Model',
             category: 'Experimental',
             requiresRestart: true,
-            default: DEFAULT_GEMINI_MODEL,
+            default: GEMINI_MODEL_ALIAS_AUTO,
             description:
               'The model to use for the Codebase Investigator agent.',
             showInDialog: false,

packages/core/src/agents/registry.test.ts

@@ -10,7 +10,13 @@ import { makeFakeConfig } from '../test-utils/config.js';
 import type { AgentDefinition } from './types.js';
 import type { Config } from '../config/config.js';
 import { debugLogger } from '../utils/debugLogger.js';
-import { DEFAULT_GEMINI_MODEL } from '../config/models.js';
+import {
+  DEFAULT_GEMINI_FLASH_LITE_MODEL,
+  GEMINI_MODEL_ALIAS_AUTO,
+  PREVIEW_GEMINI_FLASH_MODEL,
+  PREVIEW_GEMINI_MODEL,
+  PREVIEW_GEMINI_MODEL_AUTO,
+} from '../config/models.js';
 
 // A test-only subclass to expose the protected `registerAgent` method.
 class TestableAgentRegistry extends AgentRegistry {
@@ -74,12 +80,12 @@ describe('AgentRegistry', () => {
       );
     });
 
-    it('should use preview model for codebase investigator if main model is preview', async () => {
+    it('should use preview flash model for codebase investigator if main model is preview pro', async () => {
       const previewConfig = makeFakeConfig({
-        model: 'gemini-3-pro-preview',
+        model: PREVIEW_GEMINI_MODEL,
         codebaseInvestigatorSettings: {
           enabled: true,
-          model: DEFAULT_GEMINI_MODEL,
+          model: GEMINI_MODEL_ALIAS_AUTO,
         },
       });
       const previewRegistry = new TestableAgentRegistry(previewConfig);
@@ -90,7 +96,51 @@ describe('AgentRegistry', () => {
         'codebase_investigator',
       );
       expect(investigatorDef).toBeDefined();
-      expect(investigatorDef?.modelConfig.model).toBe('gemini-3-pro-preview');
+      expect(investigatorDef?.modelConfig.model).toBe(
+        PREVIEW_GEMINI_FLASH_MODEL,
+      );
+    });
+
+    it('should use preview flash model for codebase investigator if main model is preview auto', async () => {
+      const previewConfig = makeFakeConfig({
+        model: PREVIEW_GEMINI_MODEL_AUTO,
+        codebaseInvestigatorSettings: {
+          enabled: true,
+          model: GEMINI_MODEL_ALIAS_AUTO,
+        },
+      });
+      const previewRegistry = new TestableAgentRegistry(previewConfig);
+
+      await previewRegistry.initialize();
+
+      const investigatorDef = previewRegistry.getDefinition(
+        'codebase_investigator',
+      );
+      expect(investigatorDef).toBeDefined();
+      expect(investigatorDef?.modelConfig.model).toBe(
+        PREVIEW_GEMINI_FLASH_MODEL,
+      );
+    });
+
+    it('should use the model from the investigator settings', async () => {
+      const previewConfig = makeFakeConfig({
+        model: PREVIEW_GEMINI_MODEL,
+        codebaseInvestigatorSettings: {
+          enabled: true,
+          model: DEFAULT_GEMINI_FLASH_LITE_MODEL,
+        },
+      });
+      const previewRegistry = new TestableAgentRegistry(previewConfig);
+
+      await previewRegistry.initialize();
+
+      const investigatorDef = previewRegistry.getDefinition(
+        'codebase_investigator',
+      );
+      expect(investigatorDef).toBeDefined();
+      expect(investigatorDef?.modelConfig.model).toBe(
+        DEFAULT_GEMINI_FLASH_LITE_MODEL,
+      );
     });
   });
 

packages/core/src/agents/registry.ts

@@ -11,11 +11,12 @@ import { type z } from 'zod';
 import { debugLogger } from '../utils/debugLogger.js';
 import {
   DEFAULT_GEMINI_MODEL,
-  DEFAULT_GEMINI_MODEL_AUTO,
-  PREVIEW_GEMINI_MODEL,
-  PREVIEW_GEMINI_MODEL_AUTO,
+  GEMINI_MODEL_ALIAS_AUTO,
+  PREVIEW_GEMINI_FLASH_MODEL,
+  isPreviewModel,
 } from '../config/models.js';
 import type { ModelConfigAlias } from '../services/modelConfigService.js';
+import { coreEvents, CoreEvent } from '../utils/events.js';
 
 /**
  * Returns the model config alias for a given agent definition.
@@ -42,6 +43,10 @@ export class AgentRegistry {
   async initialize(): Promise<void> {
     this.loadBuiltInAgents();
 
+    coreEvents.on(CoreEvent.ModelChanged, () => {
+      this.loadBuiltInAgents();
+    });
+
     if (this.config.getDebugMode()) {
       debugLogger.log(
         `[AgentRegistry] Initialized with ${this.agents.size} agents.`,
@@ -54,23 +59,17 @@ export class AgentRegistry {
 
     // Only register the agent if it's enabled in the settings.
     if (investigatorSettings?.enabled) {
-      let model =
-        investigatorSettings.model ??
-        CodebaseInvestigatorAgent.modelConfig.model;
-
-      // If the user is using the preview model for the main agent, force the sub-agent to use it too
-      // if it's configured to use 'pro' or 'auto'.
-      if (
-        this.config.getModel() === PREVIEW_GEMINI_MODEL ||
-        this.config.getModel() === PREVIEW_GEMINI_MODEL_AUTO
-      ) {
-        if (
-          model === PREVIEW_GEMINI_MODEL_AUTO ||
-          model === DEFAULT_GEMINI_MODEL_AUTO ||
-          model === DEFAULT_GEMINI_MODEL
-        ) {
-          model = PREVIEW_GEMINI_MODEL;
-        }
+      let model;
+      const settingsModel = investigatorSettings.model;
+      // Check if the user explicitly set a model in the settings.
+      if (settingsModel && settingsModel !== GEMINI_MODEL_ALIAS_AUTO) {
+        model = settingsModel;
+      } else {
+        // Use Preview Flash model if the main model is any of the preview models
+        // If the main model is not preview model, use default pro model.
+        model = isPreviewModel(this.config.getModel())
+          ? PREVIEW_GEMINI_FLASH_MODEL
+          : DEFAULT_GEMINI_MODEL;
       }
 
       const agentDef = {

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

@@ -1704,18 +1704,16 @@ describe('Availability Service Integration', () => {
     cwd: '.',
   };
 
-  it('setActiveModel updates active model and emits event', async () => {
+  it('setActiveModel updates active model', async () => {
     const config = new Config(baseParams);
     const model1 = 'model1';
     const model2 = 'model2';
 
     config.setActiveModel(model1);
     expect(config.getActiveModel()).toBe(model1);
-    expect(mockCoreEvents.emitModelChanged).toHaveBeenCalledWith(model1);
 
     config.setActiveModel(model2);
     expect(config.getActiveModel()).toBe(model2);
-    expect(mockCoreEvents.emitModelChanged).toHaveBeenCalledWith(model2);
   });
 
   it('getActiveModel defaults to configured model if not set', () => {

packages/core/src/config/config.ts

@@ -843,7 +843,6 @@ export class Config {
   setActiveModel(model: string): void {
     if (this._activeModel !== model) {
       this._activeModel = model;
-      coreEvents.emitModelChanged(model);
     }
   }
 

packages/core/src/config/models.ts

@@ -12,6 +12,7 @@ export const DEFAULT_GEMINI_FLASH_LITE_MODEL = 'gemini-2.5-flash-lite';
 
 export const VALID_GEMINI_MODELS = new Set([
   PREVIEW_GEMINI_MODEL,
+  PREVIEW_GEMINI_FLASH_MODEL,
   DEFAULT_GEMINI_MODEL,
   DEFAULT_GEMINI_FLASH_MODEL,
   DEFAULT_GEMINI_FLASH_LITE_MODEL,
@@ -21,6 +22,7 @@ export const PREVIEW_GEMINI_MODEL_AUTO = 'auto-gemini-3';
 export const DEFAULT_GEMINI_MODEL_AUTO = 'auto-gemini-2.5';
 
 // Model aliases for user convenience.
+export const GEMINI_MODEL_ALIAS_AUTO = 'auto';
 export const GEMINI_MODEL_ALIAS_PRO = 'pro';
 export const GEMINI_MODEL_ALIAS_FLASH = 'flash';
 export const GEMINI_MODEL_ALIAS_FLASH_LITE = 'flash-lite';
@@ -124,6 +126,20 @@ export function getDisplayString(model: string) {
   }
 }
 
+/**
+ * Checks if the model is a preview model.
+ *
+ * @param model The model name to check.
+ * @returns True if the model is a preview model.
+ */
+export function isPreviewModel(model: string): boolean {
+  return (
+    model === PREVIEW_GEMINI_MODEL ||
+    model === PREVIEW_GEMINI_FLASH_MODEL ||
+    model === PREVIEW_GEMINI_MODEL_AUTO
+  );
+}
+
 /**
  * Checks if the model is a Gemini 2.x model.
  *

schemas/settings.schema.json

@@ -1361,8 +1361,8 @@
             "model": {
               "title": "Model",
               "description": "The model to use for the Codebase Investigator agent.",
-              "markdownDescription": "The model to use for the Codebase Investigator agent.\n\n- Category: `Experimental`\n- Requires restart: `yes`\n- Default: `gemini-2.5-pro`",
-              "default": "gemini-2.5-pro",
+              "markdownDescription": "The model to use for the Codebase Investigator agent.\n\n- Category: `Experimental`\n- Requires restart: `yes`\n- Default: `auto`",
+              "default": "auto",
               "type": "string"
             }
           },