Cursor

The editor people paste our key into first. If you only set up one — start here.

Three fields. Copy, don’t type

Do it in order. Don’t skip

1. Open Cursor settings: the gear at the bottom left, or Cmd + , on a Mac and Ctrl + , on Windows.

2. Search the settings for Models and open that section.

3. Find OpenAI API Key and paste the key whole, together with “sk-”.

4. Turn on Override OpenAI Base URL. Into the field that appears put the address from the card below — it must end with /v1.

5. In the model list press + Add model and paste the name exactly: claude-opus-4.8. Paste it — typing from memory is how “Opus 5” gets in, and Cursor does not know that name.

6. Untick every other model. Cursor verifies the key against whichever model is enabled, and a foreign name fails.

7. Press Verify next to the key. Green means done.

8. Open chat with Cmd + L or Ctrl + L, pick claude-opus-4.8 at the top and type “hi”.

Check

If it didn’t start

• “The model you chose is not available” with a Cloud badge and Set up Environment / Plan New Idea — that’s Cursor Cloud Agent. It never uses your key. Switch to Local Agent, new chat, model ca-fable-5.1.
• Verify won’t turn green — check that the Base URL ends with /v1 and the key is complete.
• Chat and agent work but Tab completion doesn’t — that’s Cursor by design: inline suggestions run on their own models, and your key is never used there. Same for Auto, background agents and the Cursor CLI.
• “401 / unauthorized / invalid api key” — the key was not copied whole. It starts with sk- and has no space at either end.
• “model not found” / “named models unavailable” / model in red — the name must match exactly: claude-opus-4.8. Not “Opus 5”, not opus, not claude-3, not gpt-4.
• The app shows no models — reopen its settings page: the model list is served from our address and appears once the Base URL and key are right.
• “Connection error” / spinner and silence — wrong Base URL. Almost every app wants the address with a /v1 tail.
• “/v1/v1” in the error — the app appends /v1 itself. Drop the tail, leave the site address.
• It replied, then stopped — you ran out of tokens. The balance is in your dashboard. Topping up on FunPay from the same nick lands on the same key.

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