From 8c07ad2ab905cd9c4cad428bc7f52236511d1686 Mon Sep 17 00:00:00 2001
From: joshualitt <joshualitt@google.com>
Date: Thu, 20 Nov 2025 11:19:52 -0800
Subject: [PATCH] feat(core): Use thinking level for Gemini 3 (#13445)

---
 packages/core/src/core/geminiChat.test.ts | 47 ++++++++++++++++++++++-
 packages/core/src/core/geminiChat.ts      | 25 ++++++++----
 2 files changed, 64 insertions(+), 8 deletions(-)

diff --git a/packages/core/src/core/geminiChat.test.ts b/packages/core/src/core/geminiChat.test.ts
index 6067255de0..0a6207739b 100644
--- a/packages/core/src/core/geminiChat.test.ts
+++ b/packages/core/src/core/geminiChat.test.ts
@@ -6,7 +6,7 @@
 
 import { describe, it, expect, vi, beforeEach, afterEach } from 'vitest';
 import type { Content, GenerateContentResponse } from '@google/genai';
-import { ApiError } from '@google/genai';
+import { ApiError, ThinkingLevel } from '@google/genai';
 import type { ContentGenerator } from '../core/contentGenerator.js';
 import {
   GeminiChat,
@@ -135,6 +135,9 @@ describe('GeminiChat', () => {
           model: modelConfigKey.model,
           generateContentConfig: {
             temperature: 0,
+            thinkingConfig: {
+              thinkingBudget: 1000,
+            },
           },
         })),
       },
@@ -972,12 +975,54 @@ describe('GeminiChat', () => {
             systemInstruction: '',
             tools: [],
             temperature: 0,
+            thinkingConfig: {
+              thinkingBudget: 1000,
+            },
             abortSignal: expect.any(AbortSignal),
           },
         },
         'prompt-id-1',
       );
     });
+
+    it('should use thinkingLevel and remove thinkingBudget for gemini-3 models', async () => {
+      const response = (async function* () {
+        yield {
+          candidates: [
+            {
+              content: { parts: [{ text: 'response' }], role: 'model' },
+              finishReason: 'STOP',
+            },
+          ],
+        } as unknown as GenerateContentResponse;
+      })();
+      vi.mocked(mockContentGenerator.generateContentStream).mockResolvedValue(
+        response,
+      );
+
+      const stream = await chat.sendMessageStream(
+        { model: 'gemini-3-test-only-model-string-for-testing' },
+        'hello',
+        'prompt-id-thinking-level',
+        new AbortController().signal,
+      );
+      for await (const _ of stream) {
+        // consume stream
+      }
+
+      expect(mockContentGenerator.generateContentStream).toHaveBeenCalledWith(
+        expect.objectContaining({
+          model: 'gemini-3-test-only-model-string-for-testing',
+          config: expect.objectContaining({
+            thinkingConfig: {
+              thinkingBudget: undefined,
+              thinkingLevel: ThinkingLevel.HIGH,
+            },
+          }),
+        }),
+        'prompt-id-thinking-level',
+      );
+    });
   });
 
   describe('addHistory', () => {
diff --git a/packages/core/src/core/geminiChat.ts b/packages/core/src/core/geminiChat.ts
index 8bfdcc8c03..02ce3acf60 100644
--- a/packages/core/src/core/geminiChat.ts
+++ b/packages/core/src/core/geminiChat.ts
@@ -15,6 +15,7 @@ import type {
   PartListUnion,
   GenerateContentConfig,
 } from '@google/genai';
+import { ThinkingLevel } from '@google/genai';
 import { toParts } from '../code_assist/converter.js';
 import { createUserContent, FinishReason } from '@google/genai';
 import { retryWithBackoff } from '../utils/retry.js';
@@ -412,6 +413,22 @@ export class GeminiChat {
       }
 
       effectiveModel = modelToUse;
+      const config = {
+        ...generateContentConfig,
+        // TODO(12622): Ensure we don't overrwrite these when they are
+        // passed via config.
+        systemInstruction: this.systemInstruction,
+        tools: this.tools,
+      };
+
+      // TODO(joshualitt): Clean this up with model configs.
+      if (modelToUse.startsWith('gemini-3')) {
+        config.thinkingConfig = {
+          ...config.thinkingConfig,
+          thinkingLevel: ThinkingLevel.HIGH,
+        };
+        delete config.thinkingConfig?.thinkingBudget;
+      }
 
       return this.config.getContentGenerator().generateContentStream(
         {
@@ -420,13 +437,7 @@ export class GeminiChat {
             modelToUse === PREVIEW_GEMINI_MODEL
               ? contentsForPreviewModel
               : requestContents,
-          config: {
-            ...generateContentConfig,
-            // TODO(12622): Ensure we don't overrwrite these when they are
-            // passed via config.
-            systemInstruction: this.systemInstruction,
-            tools: this.tools,
-          },
+          config,
         },
         prompt_id,
       );