Cursor API key errors — every common failure and the fix
Bringing your own key to Cursor fails in a small number of predictable ways. Almost none of them are about the key being wrong — they are about restart behaviour, doubled paths and expecting the old quota to stop immediately.
https://aicomp.ai/v1).
Create one free →
curl https://aicomp.ai/v1/models \
-H "Authorization: Bearer sk-your-gateway-key"A JSON list of model IDs means the key is good. Invalid token means it was copied wrong.
The diagnostic table
| Symptom | What is actually wrong | Fix |
|---|---|---|
| 401 invalid API key | Key truncated on paste, or copied from a partially rendered field | Regenerate, paste into a plain text editor first to confirm the full string, then into Cursor |
| Still billing the subscription | Override not saved, or not re-read yet | Save, then fully quit and relaunch — not just close the window |
| 404 on the messages path | Doubled /v1 in the base URL | If the endpoint already ends in /v1, do not add another |
| Model not found | Model name differs from what this endpoint exposes | List models with curl and copy the exact string |
| Requests hang, no error | Proxy or firewall on the endpoint host | Test with curl from the same machine; if curl also hangs it is network-level |
| Works once, then 429 | Your own per-model rate limit | Not a Cursor bug. Reduce concurrency or spread requests |
| Tool calls fail silently | Endpoint does not fully implement tool calling | Test tool use explicitly before relying on agent mode |
| Streaming arrives in one block | Endpoint buffers rather than streams | Harmless — you just lose incremental output |
Why the restart matters
When you paste your key, the connection you will later see is not necessarily the one you get — several versions only re-read overrides on a cold start. A request appearing in your gateway usage log is the only reliable proof the change took effect; the absence of a visible error is not proof of anything.
Once it works, watch cost rather than correctness
Your own key means your own bill, and Cursor generates longer prompts than most people realise — it resends file context on every request. Two things move the number more than anything else: keeping unrelated files out of context, and not routing mechanical tasks to the flagship model.
| Model | Gateway rate in / out per 1M tokens | Official list in / out per 1M tokens | Diff |
|---|---|---|---|
| claude-sonnet-5 | $1 / $5 | $2 / $10 | 50% |
| claude-haiku-4-5 | $0.5 / $2.5 | $1 / $5 | 50% |
| gpt-5.6-luna | $0.1 / $0.6 | $0.2 / $1.2 | 50% |
Rates checked 2026-09-16. Gateway rates move with upstream promotions — verify the current number in your dashboard before committing to a budget.
Still stuck
Reproduce with curl from the same machine. If curl works and Cursor does not, the problem is in the client configuration — the base URL string, or the restart. If curl fails too, it is the key or the network, and no amount of Cursor configuration will fix it.
FAQ
Why does Cursor still bill my subscription after adding my own key?
Either the override was not saved, or Cursor is still holding the old connection. Fully quit and relaunch — several versions only re-read the setting on a cold start.
The base URL field rejects my endpoint
Check for a trailing slash or a doubled /v1. Try the value you successfully used with curl, since that one is already proven correct.
It works for one request then stops
Usually rate limits on your own account rather than a Cursor problem. Cursor sends traffic faster than interactive use does, which can surface a per-model quota.
Requests hang with no error
Almost always a proxy or firewall on the endpoint host, particularly on corporate networks. Test from the same machine with curl to confirm the endpoint is reachable at all.
Can I use different models for different tasks?
Yes, once the override is active you can select any model the endpoint exposes. Match the model to the task — routing everything to the flagship is the fastest way to make your own key more expensive than the subscription.