Where does the bug appear (feature/product)? Cursor IDE Describe the Bug When using a custom LLM provider via LiteLLM proxy configured with the OpenAI-compatible /chat/completions endpoint, Cursor Agent mode sends requests in OpenAI Responses API format instead of Chat Completions format. LiteLLM’s…

Hey, thanks for the report, this is a known issue. What’s happening: when using BYOK with a base URL override, Cursor Agent sends an OpenAI Responses API payload (input, flat tool format, etc.) to the /chat/completions endpoint instead of using the Chat Completions format. Related threads about th…

Where does the bug appear (feature/product)? Cursor IDE Describe the Bug I’m trying to use a custom openai compatible provider. This looks like a bug in how Cursor is constructing the request to send to the AI provider The error is saying that the API request being sent is malformed. Specifically…

Where does the bug appear (feature/product)? Cursor IDE Describe the Bug I am new to Cursor and using it with an OpenAI-compatible base URL. I set the OpenAI Base URL and Model in the Cursor IDE under Settings → Models → API Keys. Then I clicked Toggle Agents and sent a message to GPT 5.5 with med…

It would be nice to get this prioritized and supported. There are a good number of dupes and reports spanning the past few months on this now and it’s a very opaque user experience that took me quite a while to diagnose what was going on. This behaves as if it is supported, and then fails strangely …

Hey folks, I ran into the same issue and ended up building a small bridge for this: GitHub - Pil0tXia/Cursor-OpenAI-BYOK-Bridge: Bridge Cursor OpenAI-compatible BYOK requests to... Bridge Cursor OpenAI-compatible BYOK requests to Responses API endpoints. …

Hey, thanks to both of you for the updates in this thread. @JohnPostlethwait : I agree the UX here is confusing. The setup looks supported, then it fails in a weird way. We’re tracking the issue, and extra reports help us prioritize it. I can’t share an ETA for a fix yet. When I have an update, I’ll…

Hey all! This issue appears to be fixed now. [image] GPT-5.5 BYOK not working Bug Reports Hey, good news, we’ve fixed the BYOK issue for gpt-5.5 on our side. Update to the latest version of Cursor, and requests should start going to your custom endpoint again…

This still is not working for me. I get the “User API Key Rate limit exceeded” just like I did before. The two steps are add a valid (for the endpoint) API key in the “OpenAI API Key” field, and a “Override OpenAI Bae URL” and every message I send to the GPT models gets the same “limit exceeded” mes…

Hey John, thanks for testing and getting back with the details. Quick clarification on the fix Colin mentioned. It only specifically handled routing for gpt-5.5. For other GPT models via Override OpenAI Base URL, the behavior you’re describing is still on our radar. We’re tracking the issue, but I …

Hey all, The issue should be fully resolved now. Please give it another try!

Cursor Agent sends Responses API format to /chat/completions endpoint

Support Bug Reports

Colin (Colin) June 1, 2026, 4:51pm 16

Hey all!

This issue appears to be fixed now.

Could you give it a try and let us know, just in case there’s a different issue here?

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Cursor Agent sends Responses API format to /chat/completions endpoint

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