Azure OpenAI GPT-5-Codex Not Working in Cursor (Responses API Compatibility)

Bug Reports
1

Where does the bug appear (feature/product)?

Cursor IDE

Describe the Bug

Cursor currently does not support Azure’s GPT-5-Codex deployments because the editor and agent both use the /chat/completions endpoint, while Azure’s GPT-5-Codex models only work with the newer /responses API. This makes it impossible to use GPT-5-Codex within Cursor, even though the model works perfectly through Azure’s API directly.

Add support for the Responses API in Cursor to enable compatibility with GPT-5 and GPT-5-Codex models.

(Optional) Open a beta or experimental flag for users who want to test this integration early.

Why it matters:
Many developers (myself included) run hybrid setups using Cursor + our own Azure OpenAI keys. Supporting the Responses API would unlock access to GPT-5-Codex — which is optimized for code generation, refactoring, and agentic workflows — directly inside Cursor.

Steps to Reproduce

Connect an Azure OpenAI deployment using model gpt-5-codex.

Attempt to use it in Cursor (either in the editor or Agent mode).

Cursor returns the following error:

OperationNotSupported: The chatCompletion operation does not work with the specified model, gpt-5-codex. Please choose a different model and try again.

Expected Behavior

Expected Behavior:
Cursor should detect and support models using the new /responses endpoint (used by GPT-5 and GPT-5-Codex).

Actual Behavior:
Cursor only calls /chat/completions, which causes the above error and blocks Azure GPT-5-Codex usage entirely.

Operating System

Windows 10/11

Current Cursor Version (Menu → About Cursor → Copy)

Version: 2.0.34 (user setup)
VSCode Version: 1.99.3
Commit: 45fd70f3fe72037444ba35c9e51ce86a1977ac10
Date: 2025-10-29T06:51:29.202Z
Electron: 34.5.8
Chromium: 132.0.6834.210
Node.js: 20.19.1
V8: 13.2.152.41-electron.0
OS: Windows_NT x64 10.0.26200

For AI issues: which model did you use?

codex

Additional Information

Model: gpt-5-codex (Azure OpenAI deployment)

Works fine when called directly via Azure’s /responses API

Affects both coding and agentic tasks inside Cursor

Does this stop you from using Cursor

Yes - Cursor is unusable

1 Like
2

Hey, thanks for the report. This is a known limitation with Cursor’s BYOK.

Issue: Cursor’s custom API key support currently uses the /chat/completions endpoint, which works with standard chat models. Azure GPT-5 and GPT-5-Codex deployments require the newer /responses API, which isn’t supported in Cursor BYOK yet.

Workaround: A community member built a proxy that adapts Azure’s /responses to /chat/completions: GitHub - gabrii/Cursor-Azure-GPT-5: A service that allows Cursor to use Azure GPT-5 deployments.

You can run this proxy to use your Azure GPT-5-Codex deployment with Cursor.

I’ll pass a feature request to add /responses API support for BYOK. Let us know if the workaround helps.

1 Like
3

I meet the same issue

4

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