feat(routing): restrict numerical routing to Gemini 3 family (#18478)

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

@@ -8,6 +8,7 @@ import { describe, it, expect } from 'vitest';
 import {
   resolveModel,
   resolveClassifierModel,
+  isGemini3Model,
   isGemini2Model,
   isAutoModel,
   getDisplayString,
@@ -24,6 +25,29 @@ import {
   DEFAULT_GEMINI_MODEL_AUTO,
 } from './models.js';
 
+describe('isGemini3Model', () => {
+  it('should return true for gemini-3 models', () => {
+    expect(isGemini3Model('gemini-3-pro-preview')).toBe(true);
+    expect(isGemini3Model('gemini-3-flash-preview')).toBe(true);
+  });
+
+  it('should return true for aliases that resolve to Gemini 3', () => {
+    expect(isGemini3Model(GEMINI_MODEL_ALIAS_AUTO)).toBe(true);
+    expect(isGemini3Model(GEMINI_MODEL_ALIAS_PRO)).toBe(true);
+    expect(isGemini3Model(PREVIEW_GEMINI_MODEL_AUTO)).toBe(true);
+  });
+
+  it('should return false for Gemini 2 models', () => {
+    expect(isGemini3Model('gemini-2.5-pro')).toBe(false);
+    expect(isGemini3Model('gemini-2.5-flash')).toBe(false);
+    expect(isGemini3Model(DEFAULT_GEMINI_MODEL_AUTO)).toBe(false);
+  });
+
+  it('should return false for arbitrary strings', () => {
+    expect(isGemini3Model('gpt-4')).toBe(false);
+  });
+});
+
 describe('getDisplayString', () => {
   it('should return Auto (Gemini 3) for preview auto model', () => {
     expect(getDisplayString(PREVIEW_GEMINI_MODEL_AUTO)).toBe('Auto (Gemini 3)');

packages/core/src/config/models.ts

@@ -120,6 +120,17 @@ export function isPreviewModel(model: string): boolean {
   );
 }
 
+/**
+ * Checks if the model is a Gemini 3 model.
+ *
+ * @param model The model name to check.
+ * @returns True if the model is a Gemini 3 model.
+ */
+export function isGemini3Model(model: string): boolean {
+  const resolved = resolveModel(model);
+  return /^gemini-3(\.|-|$)/.test(resolved);
+}
+
 /**
  * Checks if the model is a Gemini 2.x model.
  *

packages/core/src/routing/strategies/classifierStrategy.test.ts

@@ -17,6 +17,7 @@ import {
   DEFAULT_GEMINI_FLASH_MODEL,
   DEFAULT_GEMINI_MODEL,
   DEFAULT_GEMINI_MODEL_AUTO,
+  PREVIEW_GEMINI_MODEL_AUTO,
 } from '../../config/models.js';
 import { promptIdContext } from '../../utils/promptIdContext.js';
 import type { Content } from '@google/genai';
@@ -50,7 +51,7 @@ describe('ClassifierStrategy', () => {
       modelConfigService: {
         getResolvedConfig: vi.fn().mockReturnValue(mockResolvedConfig),
       },
-      getModel: () => DEFAULT_GEMINI_MODEL_AUTO,
+      getModel: vi.fn().mockReturnValue(DEFAULT_GEMINI_MODEL_AUTO),
       getNumericalRoutingEnabled: vi.fn().mockResolvedValue(false),
     } as unknown as Config;
     mockBaseLlmClient = {
@@ -60,8 +61,9 @@ describe('ClassifierStrategy', () => {
     vi.spyOn(promptIdContext, 'getStore').mockReturnValue('test-prompt-id');
   });
 
-  it('should return null if numerical routing is enabled', async () => {
+  it('should return null if numerical routing is enabled and model is Gemini 3', async () => {
     vi.mocked(mockConfig.getNumericalRoutingEnabled).mockResolvedValue(true);
+    vi.mocked(mockConfig.getModel).mockReturnValue(PREVIEW_GEMINI_MODEL_AUTO);
 
     const decision = await strategy.route(
       mockContext,
@@ -73,6 +75,24 @@ describe('ClassifierStrategy', () => {
     expect(mockBaseLlmClient.generateJson).not.toHaveBeenCalled();
   });
 
+  it('should NOT return null if numerical routing is enabled but model is NOT Gemini 3', async () => {
+    vi.mocked(mockConfig.getNumericalRoutingEnabled).mockResolvedValue(true);
+    vi.mocked(mockConfig.getModel).mockReturnValue(DEFAULT_GEMINI_MODEL_AUTO);
+    vi.mocked(mockBaseLlmClient.generateJson).mockResolvedValue({
+      reasoning: 'test',
+      model_choice: 'flash',
+    });
+
+    const decision = await strategy.route(
+      mockContext,
+      mockConfig,
+      mockBaseLlmClient,
+    );
+
+    expect(decision).not.toBeNull();
+    expect(mockBaseLlmClient.generateJson).toHaveBeenCalled();
+  });
+
   it('should call generateJson with the correct parameters', async () => {
     const mockApiResponse = {
       reasoning: 'Simple task',

packages/core/src/routing/strategies/classifierStrategy.ts

@@ -12,7 +12,7 @@ import type {
   RoutingDecision,
   RoutingStrategy,
 } from '../routingStrategy.js';
-import { resolveClassifierModel } from '../../config/models.js';
+import { resolveClassifierModel, isGemini3Model } from '../../config/models.js';
 import { createUserContent, Type } from '@google/genai';
 import type { Config } from '../../config/config.js';
 import {
@@ -133,7 +133,11 @@ export class ClassifierStrategy implements RoutingStrategy {
   ): Promise<RoutingDecision | null> {
     const startTime = Date.now();
     try {
-      if (await config.getNumericalRoutingEnabled()) {
+      const model = context.requestedModel ?? config.getModel();
+      if (
+        (await config.getNumericalRoutingEnabled()) &&
+        isGemini3Model(model)
+      ) {
         return null;
       }
 
@@ -164,7 +168,7 @@ export class ClassifierStrategy implements RoutingStrategy {
       const reasoning = routerResponse.reasoning;
       const latencyMs = Date.now() - startTime;
       const selectedModel = resolveClassifierModel(
-        context.requestedModel ?? config.getModel(),
+        model,
         routerResponse.model_choice,
       );
 

packages/core/src/routing/strategies/numericalClassifierStrategy.test.ts

@@ -10,9 +10,11 @@ import type { RoutingContext } from '../routingStrategy.js';
 import type { Config } from '../../config/config.js';
 import type { BaseLlmClient } from '../../core/baseLlmClient.js';
 import {
-  DEFAULT_GEMINI_FLASH_MODEL,
+  PREVIEW_GEMINI_FLASH_MODEL,
-  DEFAULT_GEMINI_MODEL,
+  PREVIEW_GEMINI_MODEL,
+  PREVIEW_GEMINI_MODEL_AUTO,
   DEFAULT_GEMINI_MODEL_AUTO,
+  DEFAULT_GEMINI_MODEL,
 } from '../../config/models.js';
 import { promptIdContext } from '../../utils/promptIdContext.js';
 import type { Content } from '@google/genai';
@@ -46,7 +48,7 @@ describe('NumericalClassifierStrategy', () => {
       modelConfigService: {
         getResolvedConfig: vi.fn().mockReturnValue(mockResolvedConfig),
       },
-      getModel: () => DEFAULT_GEMINI_MODEL_AUTO,
+      getModel: vi.fn().mockReturnValue(PREVIEW_GEMINI_MODEL_AUTO),
       getSessionId: vi.fn().mockReturnValue('control-group-id'), // Default to Control Group (Hash 71 >= 50)
       getNumericalRoutingEnabled: vi.fn().mockResolvedValue(true),
       getClassifierThreshold: vi.fn().mockResolvedValue(undefined),
@@ -75,6 +77,32 @@ describe('NumericalClassifierStrategy', () => {
     expect(mockBaseLlmClient.generateJson).not.toHaveBeenCalled();
   });
 
+  it('should return null if the model is not a Gemini 3 model', async () => {
+    vi.mocked(mockConfig.getModel).mockReturnValue(DEFAULT_GEMINI_MODEL_AUTO);
+
+    const decision = await strategy.route(
+      mockContext,
+      mockConfig,
+      mockBaseLlmClient,
+    );
+
+    expect(decision).toBeNull();
+    expect(mockBaseLlmClient.generateJson).not.toHaveBeenCalled();
+  });
+
+  it('should return null if the model is explicitly a Gemini 2 model', async () => {
+    vi.mocked(mockConfig.getModel).mockReturnValue(DEFAULT_GEMINI_MODEL);
+
+    const decision = await strategy.route(
+      mockContext,
+      mockConfig,
+      mockBaseLlmClient,
+    );
+
+    expect(decision).toBeNull();
+    expect(mockBaseLlmClient.generateJson).not.toHaveBeenCalled();
+  });
+
   it('should call generateJson with the correct parameters and wrapped user content', async () => {
     const mockApiResponse = {
       complexity_reasoning: 'Simple task',
@@ -119,7 +147,7 @@ describe('NumericalClassifierStrategy', () => {
       );
 
       expect(decision).toEqual({
-        model: DEFAULT_GEMINI_FLASH_MODEL,
+        model: PREVIEW_GEMINI_FLASH_MODEL,
         metadata: {
           source: 'NumericalClassifier (Control)',
           latencyMs: expect.any(Number),
@@ -145,7 +173,7 @@ describe('NumericalClassifierStrategy', () => {
       );
 
       expect(decision).toEqual({
-        model: DEFAULT_GEMINI_MODEL,
+        model: PREVIEW_GEMINI_MODEL,
         metadata: {
           source: 'NumericalClassifier (Control)',
           latencyMs: expect.any(Number),
@@ -171,7 +199,7 @@ describe('NumericalClassifierStrategy', () => {
       );
 
       expect(decision).toEqual({
-        model: DEFAULT_GEMINI_FLASH_MODEL, // Routed to Flash because 60 < 80
+        model: PREVIEW_GEMINI_FLASH_MODEL, // Routed to Flash because 60 < 80
         metadata: {
           source: 'NumericalClassifier (Strict)',
           latencyMs: expect.any(Number),
@@ -197,7 +225,7 @@ describe('NumericalClassifierStrategy', () => {
       );
 
       expect(decision).toEqual({
-        model: DEFAULT_GEMINI_MODEL,
+        model: PREVIEW_GEMINI_MODEL,
         metadata: {
           source: 'NumericalClassifier (Strict)',
           latencyMs: expect.any(Number),
@@ -225,7 +253,7 @@ describe('NumericalClassifierStrategy', () => {
       );
 
       expect(decision).toEqual({
-        model: DEFAULT_GEMINI_FLASH_MODEL, // Score 60 < Threshold 70
+        model: PREVIEW_GEMINI_FLASH_MODEL, // Score 60 < Threshold 70
         metadata: {
           source: 'NumericalClassifier (Remote)',
           latencyMs: expect.any(Number),
@@ -251,7 +279,7 @@ describe('NumericalClassifierStrategy', () => {
       );
 
       expect(decision).toEqual({
-        model: DEFAULT_GEMINI_FLASH_MODEL, // Score 40 < Threshold 45.5
+        model: PREVIEW_GEMINI_FLASH_MODEL, // Score 40 < Threshold 45.5
         metadata: {
           source: 'NumericalClassifier (Remote)',
           latencyMs: expect.any(Number),
@@ -277,7 +305,7 @@ describe('NumericalClassifierStrategy', () => {
       );
 
       expect(decision).toEqual({
-        model: DEFAULT_GEMINI_MODEL, // Score 35 >= Threshold 30
+        model: PREVIEW_GEMINI_MODEL, // Score 35 >= Threshold 30
         metadata: {
           source: 'NumericalClassifier (Remote)',
           latencyMs: expect.any(Number),
@@ -305,7 +333,7 @@ describe('NumericalClassifierStrategy', () => {
       );
 
       expect(decision).toEqual({
-        model: DEFAULT_GEMINI_FLASH_MODEL, // Score 40 < Default A/B Threshold 50
+        model: PREVIEW_GEMINI_FLASH_MODEL, // Score 40 < Default A/B Threshold 50
         metadata: {
           source: 'NumericalClassifier (Control)',
           latencyMs: expect.any(Number),
@@ -332,7 +360,7 @@ describe('NumericalClassifierStrategy', () => {
       );
 
       expect(decision).toEqual({
-        model: DEFAULT_GEMINI_FLASH_MODEL,
+        model: PREVIEW_GEMINI_FLASH_MODEL,
         metadata: {
           source: 'NumericalClassifier (Control)',
           latencyMs: expect.any(Number),
@@ -359,7 +387,7 @@ describe('NumericalClassifierStrategy', () => {
       );
 
       expect(decision).toEqual({
-        model: DEFAULT_GEMINI_MODEL,
+        model: PREVIEW_GEMINI_MODEL,
         metadata: {
           source: 'NumericalClassifier (Control)',
           latencyMs: expect.any(Number),

packages/core/src/routing/strategies/numericalClassifierStrategy.ts

@@ -12,7 +12,7 @@ import type {
   RoutingDecision,
   RoutingStrategy,
 } from '../routingStrategy.js';
-import { resolveClassifierModel } from '../../config/models.js';
+import { resolveClassifierModel, isGemini3Model } from '../../config/models.js';
 import { createUserContent, Type } from '@google/genai';
 import type { Config } from '../../config/config.js';
 import { debugLogger } from '../../utils/debugLogger.js';
@@ -134,10 +134,15 @@ export class NumericalClassifierStrategy implements RoutingStrategy {
   ): Promise<RoutingDecision | null> {
     const startTime = Date.now();
     try {
+      const model = context.requestedModel ?? config.getModel();
       if (!(await config.getNumericalRoutingEnabled())) {
         return null;
       }
 
+      if (!isGemini3Model(model)) {
+        return null;
+      }
+
       const promptId = getPromptIdWithFallback('classifier-router');
 
       const finalHistory = context.history.slice(-HISTORY_TURNS_FOR_CONTEXT);
@@ -176,10 +181,7 @@ export class NumericalClassifierStrategy implements RoutingStrategy {
           config.getSessionId() || 'unknown-session',
         );
 
-      const selectedModel = resolveClassifierModel(
+      const selectedModel = resolveClassifierModel(model, modelAlias);
-        config.getModel(),
-        modelAlias,
-      );
 
       const latencyMs = Date.now() - startTime;