Hey, thanks for the report. OpenRouter isn’t officially supported in Cursor, so new models like Gemini 3 Pro Preview via OpenRouter often fail with request format errors (for example, a required thought_signature). Confirmation and details here: Cursor is practically unusable with any new model through OpenRouter
What you can do:
- Use built-in Cursor Pro models
- Or add an official provider API key in Settings → Models: Google (for Gemini), Anthropic, OpenAI, Azure, AWS Bedrock - API Keys | Cursor Docs
Could you try a Google AI key for Gemini and let us know if it helps? If the issue remains after that, please share a screenshot of the error and the new Request ID.