Custom api provider url/payload format error

Support Bug Reports
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1

Where does the bug appear (feature/product)?

Cursor IDE

Describe the Bug

why can not custom api provider choose api endpoint? it is always ‘/chat/compleions’ , while payload format is for response api

Steps to Reproduce

I customized my own api provider which supports openai api, and when I use ide to edit, it shows :Provider returned error: {“error”:{“message”:“field messages is required (request id: 20260330155022925846949KWcCHXhT)”,“type”:“rix_api_error”,“param”:“”,“code”:“invalid_request”}}

Operating System

Windows 10/11

Version Information

Version: 2.6.22 (user setup)
VSCode Version: 1.105.1
Commit: c6285feaba0ad62603f7c22e72f0a170dc8415a0
Date: 2026-03-27T15:59:31.561Z
Build Type: Stable
Release Track: Default
Electron: 39.8.1
Chromium: 142.0.7444.265
Node.js: 22.22.1
V8: 14.2.231.22-electron.0
OS: Windows_NT x64 10.0.26200

For AI issues: which model did you use?

gpt-5.4

For AI issues: add Request ID with privacy disabled

8c5d5bb0-e2c9-4224-bf8c-b020c9e984f3

Does this stop you from using Cursor

Yes - Cursor is unusable

4

Hey, this is a known issue. When you use a custom API provider, Cursor sends a payload in the Responses API format (input instead of messages, flat tools format, etc.) to the /chat/completions endpoint. That’s why you get the error “field messages is required”.

More details here: Cursor Agent sends Responses API format to /chat/completions endpoint

The team is aware. There’s no timeline for a fix yet, but your report helps with prioritization.

For now, the main workaround is to intercept and convert the payload on the proxy side (Responses API to Chat Completions format). If your provider can’t support that, you can try using Cursor’s built-in routing instead of a base URL override.