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

[Colin]

Hi @KungFuPanda!

This looks like the same issue as over here, and it should be something you can fix if you’re forwarding the requests yourself.

OpenAI / ChatGPT BYOK models abort after brief reply in Cursor

Thanks a lot for taking the time, I hope this reply helps: I dug into the traffic on my side and can confirm the ApplyPatch custom tool isn’t surviving the round trip. My endpoint sits in front of an upstream that speaks the newer Responses-style API, so requests get translated on the way there and the reply gets translated back into chat/completions for Cursor. The translation back is where it breaks: The request going upstream is fine — the type:"custom" ApplyPatch tool passes through and t…