Hey, thanks for the report. OpenRouter is not officially supported in Cursor right now - this is a known limitation. When you enable “Override OpenAI Base URL” with OpenRouter, Cursor sends malformed requests, which is why you see authentication errors.
Supported BYOK providers:
- OpenAI
- Anthropic
- Azure OpenAI
- AWS Bedrock
The team is aware of the OpenRouter issue and is working on proper support for custom OpenAI‑compatible endpoints, but there’s no concrete timeline yet.
For now, the most reliable option is to use a direct Anthropic API connection.