Before you connect
Create a dedicated key, check the live model list and confirm that your Cursor version supports a custom compatible endpoint for the workflow you intend to use. Do not paste a production key into screenshots or issue trackers.
Cursor's BYOK behavior can differ between chat, agent and specialized features. Treat compatibility as a tested path, not a promise that every built-in feature will use the custom endpoint.
Use a constrained key
Allow only the model you plan to test, set a low daily spend cap and keep concurrency small. A coding agent can produce long contexts and repeated tool loops, so start with a limit you can inspect safely.
Verify with one small request
Send a short test request, confirm the response and then check the Model.sale usage log. Match the request ID, model, terminal tokens and charge. If the request does not appear, stop and fix the endpoint before increasing traffic.
Test streaming and cancellation separately. Close one response mid-stream, then confirm that the reservation is released or reconciled according to the recorded terminal state.
Common failure modes
If Cursor reports 401, verify the base URL and Bearer key without posting either publicly. A 429 can come from RPM, TPM, concurrency or spend protection. A model-not-found error usually means the client is sending a display name instead of the exact public model ID.
Rotate cleanly
When a key has been shared or a team member leaves, revoke it and create a replacement. The dashboard keeps the prefix and status visible without storing the complete secret.
Keep development and production keys separate. After rotation, verify that the old key returns 401 and the new key appears as a distinct prefix in usage records.