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…

Hey, thanks for the detailed report. The proxy-level breakdown path vs body vs parser is super helpful. This is a known bug. When you use Override OpenAI Base URL with models that go through the Responses API path GPT-5 family, o3, o4, gpt-4*, Cursor sends a Responses-shaped body to /chat/completio…

Override OpenAI Base URL sends Responses API payload to /chat/completions but expects Chat Completions output

Support Bug Reports

Topic		Replies	Views
It's a communication error between Cursor and the Openai compatible provider Bug Reports byok , openai	1	104	April 24, 2026
YOK: GPT-5.6 reasoning content not shown even when returned by OpenAI Bug Reports byok , openai	1	130	July 12, 2026
BYOK does not send the "reasoning_effort" parameter for GPT-5.6 models Bug Reports byok , openai	5	137	August 2, 2026
5.5 custom base url model bug Bug Reports byok , openai	3	126	May 14, 2026
Cursor Agent sends Responses API format to /chat/completions endpoint Bug Reports byok , openai	12	1482	July 9, 2026

Override OpenAI Base URL sends Responses API payload to /chat/completions but expects Chat Completions output

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