From f2bddfe054f83ef7e93b262fadc03554abf3ba64 Mon Sep 17 00:00:00 2001
From: Pyush Sinha <pyushsinha20@gmail.com>
Date: Fri, 29 Aug 2025 09:20:50 -0700
Subject: [PATCH] fix: add flash lite with respect to api defaults (#4652)

Co-authored-by: Gal Zahavi <38544478+galz10@users.noreply.github.com>
---
 packages/core/src/config/models.ts    |  3 ++
 packages/core/src/core/client.test.ts | 41 ++++++++++++++++++++++++++-
 packages/core/src/core/client.ts      | 21 ++++++++++----
 3 files changed, 59 insertions(+), 6 deletions(-)

diff --git a/packages/core/src/config/models.ts b/packages/core/src/config/models.ts
index 175f05795d..1d2c1310a7 100644
--- a/packages/core/src/config/models.ts
+++ b/packages/core/src/config/models.ts
@@ -9,3 +9,6 @@ export const DEFAULT_GEMINI_FLASH_MODEL = 'gemini-2.5-flash';
 export const DEFAULT_GEMINI_FLASH_LITE_MODEL = 'gemini-2.5-flash-lite';
 
 export const DEFAULT_GEMINI_EMBEDDING_MODEL = 'gemini-embedding-001';
+
+// Some thinking models do not default to dynamic thinking which is done by a value of -1
+export const DEFAULT_THINKING_MODE = -1;
diff --git a/packages/core/src/core/client.test.ts b/packages/core/src/core/client.test.ts
index 8f37c2dcc9..3aea7ad9f6 100644
--- a/packages/core/src/core/client.test.ts
+++ b/packages/core/src/core/client.test.ts
@@ -22,7 +22,12 @@ import type {
   Part,
 } from '@google/genai';
 import { GoogleGenAI } from '@google/genai';
-import { findIndexAfterFraction, GeminiClient } from './client.js';
+import {
+  findIndexAfterFraction,
+  isThinkingDefault,
+  isThinkingSupported,
+  GeminiClient,
+} from './client.js';
 import {
   AuthType,
   type ContentGenerator,
@@ -162,6 +167,40 @@ describe('findIndexAfterFraction', () => {
   });
 });
 
+describe('isThinkingSupported', () => {
+  it('should return true for gemini-2.5', () => {
+    expect(isThinkingSupported('gemini-2.5')).toBe(true);
+  });
+
+  it('should return true for gemini-2.5-pro', () => {
+    expect(isThinkingSupported('gemini-2.5-pro')).toBe(true);
+  });
+
+  it('should return false for other models', () => {
+    expect(isThinkingSupported('gemini-1.5-flash')).toBe(false);
+    expect(isThinkingSupported('some-other-model')).toBe(false);
+  });
+});
+
+describe('isThinkingDefault', () => {
+  it('should return false for gemini-2.5-flash-lite', () => {
+    expect(isThinkingDefault('gemini-2.5-flash-lite')).toBe(false);
+  });
+
+  it('should return true for gemini-2.5', () => {
+    expect(isThinkingDefault('gemini-2.5')).toBe(true);
+  });
+
+  it('should return true for gemini-2.5-pro', () => {
+    expect(isThinkingDefault('gemini-2.5-pro')).toBe(true);
+  });
+
+  it('should return false for other models', () => {
+    expect(isThinkingDefault('gemini-1.5-flash')).toBe(false);
+    expect(isThinkingDefault('some-other-model')).toBe(false);
+  });
+});
+
 describe('Gemini Client (client.ts)', () => {
   let client: GeminiClient;
   beforeEach(async () => {
diff --git a/packages/core/src/core/client.ts b/packages/core/src/core/client.ts
index 7f2abd694d..c9cf597daa 100644
--- a/packages/core/src/core/client.ts
+++ b/packages/core/src/core/client.ts
@@ -36,7 +36,10 @@ import type {
 } from './contentGenerator.js';
 import { AuthType, createContentGenerator } from './contentGenerator.js';
 import { ProxyAgent, setGlobalDispatcher } from 'undici';
-import { DEFAULT_GEMINI_FLASH_MODEL } from '../config/models.js';
+import {
+  DEFAULT_GEMINI_FLASH_MODEL,
+  DEFAULT_THINKING_MODE,
+} from '../config/models.js';
 import { LoopDetectionService } from '../services/loopDetectionService.js';
 import { ideContext } from '../ide/ideContext.js';
 import {
@@ -51,7 +54,13 @@ import {
 } from '../telemetry/types.js';
 import type { IdeContext, File } from '../ide/ideContext.js';
 
-function isThinkingSupported(model: string) {
+export function isThinkingSupported(model: string) {
+  if (model.startsWith('gemini-2.5')) return true;
+  return false;
+}
+
+export function isThinkingDefault(model: string) {
+  if (model.startsWith('gemini-2.5-flash-lite')) return false;
   if (model.startsWith('gemini-2.5')) return true;
   return false;
 }
@@ -245,14 +254,16 @@ export class GeminiClient {
     try {
       const userMemory = this.config.getUserMemory();
       const systemInstruction = getCoreSystemPrompt(userMemory);
-      const generateContentConfigWithThinking = isThinkingSupported(
-        this.config.getModel(),
-      )
+      const model = this.config.getModel();
+      const generateContentConfigWithThinking = isThinkingSupported(model)
         ? {
             ...this.generateContentConfig,
             thinkingConfig: {
               thinkingBudget: -1,
               includeThoughts: true,
+              ...(!isThinkingDefault(model)
+                ? { thinkingBudget: DEFAULT_THINKING_MODE }
+                : {}),
             },
           }
         : this.generateContentConfig;