Coding tools

Cursor

Beta

Use Deference models in Cursor through its OpenAI key override. In beta.

Cursor can send chat requests to an OpenAI-compatible base URL. This integration is in beta: Cursor's tool-call format and its handling of custom models change between releases.

Set up

Create a key in API keys.
In Cursor, open Settings, then Models.
Under API Keys, turn on OpenAI API Key and paste your sk-df-... key.
Turn on Override OpenAI Base URL and enter https://deference.si/v1.
Select Add model and enter an exact id from the Models page, for example anthropic/claude-sonnet-5.5.
Pick the model in the chat model picker.

Cursor reads the key from this screen only. There is no environment variable or file for it.

Verify

Open a chat in Ask mode, pick the model you added and send a prompt. Then open Activity. The request is the top row, with the endpoint Chat completions and the model you added.

Know the limits

Requests go through Cursor's servers, so the base URL must be public. https://deference.si/v1 is. A local or private address fails.
Tab completion never uses your key.
Cursor's zero data retention setting does not apply to requests sent with your own key.
The override is global. While it is on, Cursor can send its own OpenAI models to Deference too, and they fail there. Turn the override off to use Cursor's models.
Ask mode is the most reliable. Agent mode sends tool definitions and Responses-style payloads that depend on the model and the Cursor version, so try another model if tool calls fail.

Troubleshooting

You see	Cause	Fix
No Override OpenAI Base URL toggle	Cursor does not show it on every plan or version	Update Cursor and check your plan
Cursor rejects the model name	The id differs from the catalog	Copy the id from the Models page
`401 invalid_api_key`	The key field holds extra characters	Paste the key again
Agent mode fails on tool calls, or returns a blank error	Cursor's Agent payload does not suit the model	Use Ask mode, pick another model, or set Settings, Network, HTTP Compatibility Mode to HTTP/1.1
A Cursor model says it is not available	The override captures Cursor's own OpenAI models	Turn off Override OpenAI Base URL
The override does not apply	The toggle is off	Turn on Override OpenAI Base URL
`402 insufficient_credit`	No available credit	Add credit