Fix: [Bug]: Gemini Image Generation: imageConfig parameters (imageSize, aspectRatio) are completely ignored #18656

litellm/llms/gemini/google_genai/transformation.py

@@ -89,6 +89,7 @@ class GoogleGenAIConfig(BaseGoogleGenAIGenerateContentConfig, VertexLLM):
             "audio_timestamp",
             "automatic_function_calling",
             "thinking_config",
+            "image_config",
         ]
 
     def map_generate_content_optional_params(

litellm/proxy/google_endpoints/endpoints.py

@@ -37,6 +37,11 @@ async def google_generate_content(
     if "model" not in data:
         data["model"] = model_name
     
+    # Extract generationConfig and pass it as config parameter
+    generation_config = data.pop("generationConfig", None)
+    if generation_config:
+        data["config"] = generation_config
+    
     # Add user authentication metadata for cost tracking
     data = await add_litellm_data_to_request(
         data=data,
@@ -83,6 +88,11 @@ async def google_stream_generate_content(
 
     data["stream"] = True  # enforce streaming for this endpoint
 
+    # Extract generationConfig and pass it as config parameter
+    generation_config = data.pop("generationConfig", None)
+    if generation_config:
+        data["config"] = generation_config
+
     # Add user authentication metadata for cost tracking
     data = await add_litellm_data_to_request(
         data=data,

tests/test_litellm/proxy/google_endpoints/test_google_api_endpoints.py

@@ -306,6 +306,88 @@ def test_google_generate_content_with_system_instruction():
         assert called_data["systemInstruction"] == system_instruction
         assert called_data["systemInstruction"]["parts"][0]["text"] == "Your name is Doodle."
         
+        # Verify contents are also present
+        assert "contents" in called_data
+        assert len(called_data["contents"]) == 1
+        assert called_data["contents"][0]["role"] == "user"
+
+
+def test_google_generate_content_with_image_config():
+    """
+    Test that imageConfig is correctly passed through from generationConfig to the router.
+    
+    This test verifies that imageConfig parameters (aspectRatio, imageSize) are preserved
+    when forwarding requests to Google GenAI through the endpoint.
+    """
+    try:
+        from fastapi import FastAPI
+        from fastapi.testclient import TestClient
+
+        from litellm.proxy.google_endpoints.endpoints import router as google_router
+    except ImportError as e:
+        pytest.skip(f"Skipping test due to missing dependency: {e}")
+    
+    # Create a FastAPI app and include the router
+    app = FastAPI()
+    app.include_router(google_router)
+    
+    # Create a test client
+    client = TestClient(app)
+    
+    # Mock all required proxy server dependencies
+    with patch("litellm.proxy.proxy_server.llm_router") as mock_router, \
+         patch("litellm.proxy.proxy_server.general_settings", {}), \
+         patch("litellm.proxy.proxy_server.proxy_config") as mock_proxy_config, \
+         patch("litellm.proxy.proxy_server.version", "1.0.0"), \
+         patch("litellm.proxy.litellm_pre_call_utils.add_litellm_data_to_request") as mock_add_data:
+        
+        mock_router.agenerate_content = AsyncMock(return_value={"test": "response"})
+        
+        # Mock add_litellm_data_to_request to pass through data unchanged
+        async def mock_add_litellm_data(data, request, user_api_key_dict, proxy_config, general_settings, version):
+            return data
+        
+        mock_add_data.side_effect = mock_add_litellm_data
+        
+        # Send a request with generationConfig containing imageConfig
+        response = client.post(
+            "/v1beta/models/gemini-3-pro-image-preview:generateContent",
+            json={
+                "contents": [{
+                    "role": "user",
+                    "parts": [{"text": "Create a vibrant infographic about photosynthesis"}]
+                }],
+                "generationConfig": {
+                    "responseModalities": ["TEXT", "IMAGE"],
+                    "imageConfig": {
+                        "aspectRatio": "9:16",
+                        "imageSize": "4K"
+                    }
+                }
+            },
+            headers={"Authorization": "Bearer sk-test-key"}
+        )
+        
+        # Verify the response
+        assert response.status_code == 200
+        
+        # Verify that agenerate_content was called
+        mock_router.agenerate_content.assert_called_once()
+        call_args = mock_router.agenerate_content.call_args
+        called_data = call_args[1]
+        
+        # Verify that config is present in the call arguments
+        assert "config" in called_data
+        
+        # Verify that imageConfig is preserved in the config
+        assert "imageConfig" in called_data["config"]
+        assert called_data["config"]["imageConfig"]["aspectRatio"] == "9:16"
+        assert called_data["config"]["imageConfig"]["imageSize"] == "4K"
+        
+        # Verify that responseModalities is also preserved
+        assert "responseModalities" in called_data["config"]
+        assert called_data["config"]["responseModalities"] == ["TEXT", "IMAGE"]
+        
         # Verify contents are also present
         assert "contents" in called_data
         assert len(called_data["contents"]) == 1