Describe the Bug
Anthropic models don’t work correctly in Agent mode, when called with OpenRouter
Steps to Reproduce
- Issue an API key at OpenRouter:
https://openrouter.ai/settings/keys
- In cursor settings → Models turn on “Open API key”, insert the key
- Override OpenAI Base URL:
https://openrouter.ai/api/v1
- Click Verify
- In the models list add a custom model anthropic/claude-sonnet-4 and activate it
- start a new chat, choose the model for the chat, choose Agent mode, prompt something
Cursor outputs raw, unprocessed text output from the model, tool calls are not processed. It also prints an error: Model anthropic/claude-sonnet-4 doesn’t have good agent support yet. Start a new thread using Manual mode for better results.
Expected Behavior
Cursor uses the model in Agent mode, processes the tool calling correctly and formatting the output accordingly
Screenshots / Screen Recordings
Operating System
MacOS
Current Cursor Version (Menu → About Cursor → Copy)
Version: 1.0.0
VSCode Version: 1.96.2
Commit: 53b99ce608cba35127ae3a050c1738a959750860
Date: 2025-06-04T19:21:39.410Z
Electron: 34.5.1
Chromium: 132.0.6834.210
Node.js: 20.19.0
V8: 13.2.152.41-electron.0
OS: Darwin x64 24.5.0
Additional Information
I have not tested it with models from other vendors run with openrouter
Does this stop you from using Cursor
No - Cursor works, but with this issue