Use Redline in Cursor (with caveats)
Cursor can be pointed at Redline, but only partly, and the working method comes from Cursor staff on the forum rather than the official BYOK docs. Read the limits before you rely on it.
Override the OpenAI base URL
In Cursor, open Settings, then Models. Turn on "Override OpenAI Base URL" and set it to https://redline-gateway.pages.dev/v1. Paste your key into the "OpenAI API Key" field, then add your model id under Custom Models (for example deepseek/deepseek-chat-v3.1).
What does not work Cursor's official BYOK docs list only OpenAI, Anthropic, Google, Azure and Bedrock and never mention a base-URL override; the override lives in the UI and is confirmed by Cursor staff on the forum, not in the docs. Composer models reject custom keys. Tab (autocomplete) stays on Cursor's own models. The override is global, so it also repoints Cursor's built-in models until you toggle it back. Background agents and the cursor-agent CLI do not honour it.
If your work is chat and agent edits with a custom model, this works. If you need Composer or Tab, Cursor is not the tool to run Redline through, and one of the other agents will serve you better.