Cursor API key errors — every common failure and the fix

By the aitokensai editors · Verified 2026-11-01 Sources: Cursor docs

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.

In short: Most Cursor own-key failures are not invalid keys. They are: the base URL override only being re-read on a cold start (so a full quit is required), a doubled /v1 producing a 404, and expecting subscription billing to stop when it has not. A request appearing in your gateway usage log is the only reliable proof the override took effect.

You need a key before the code below runs. Create an account, generate a key, and copy the base URL (https://aicomp.ai/v1). Create one free →

Check current rates → Free to sign up · $1 minimum top-up · No prepayment

Confirm the key works first. One command, no SDK, costs nothing:

Don't have an account yet? You need an API key from the gateway before the steps below will work — how the discount works and what you take on. Create one free → (no prepay, $1 minimum top-up)

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.

Rates for the models commonly used from Cursor — USD per 1M tokens
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 2026-11-01. Gateway rates move with upstream promotions, verify the current number in your dashboard before committing to a budget.

Cost note. If a task is mechanical (rename, refactor, formatting) the cheaper tier handles it and the difference compounds over hundreds of requests. When stepping up genuinely matters, architectural decisions, multi-file reasoning, the flagship pays for itself.

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.

Why "no error" is not the same as "working"

Three things look identical from inside the editor: the override took effect, the override was ignored, and the override was read but the request was rejected somewhere upstream. Only one of them means your own key is being used. The way to separate them is to look at the usage log rather than at the editor, a request that appears there is proof, and the absence of a visible error is not proof of anything.

This matters because the failure is financial rather than functional. If the override did not take, your work is still being billed to the subscription you were trying to move away from, and every request succeeds while doing so. Nothing in the UI distinguishes that from success.

# Test from the shell so the editor is not part of the equation.
# If this works and the editor does not, the fault is in the client config --
# the override string or the restart -- not in the key or the network.

BASE="https://aicomp.ai/v1"
KEY="$GATEWAY_API_KEY"

echo "--- does the endpoint answer at all, and is the key accepted?"
curl -sS -o /dev/null -w "models: %{http_code}\n" "$BASE/models" -H "Authorization: Bearer $KEY"

echo "--- is the path shape right? (404 here = doubled or missing /v1)"
curl -sS -o /dev/null -w "no key: %{http_code}\n" "$BASE/models"      # 401 = path resolves
curl -sS -o /dev/null -w "bad path: %{http_code}\n" "$BASE/v1/models" # 404 = shape is wrong

echo "--- which model IDs does it actually serve?"
curl -sS "$BASE/models" -H "Authorization: Bearer $KEY" | grep -o '"id":"[^"]*"' | head -20

echo "--- then confirm in the usage log, not in the editor:"
echo "    a request appearing there is the only proof the override took effect.

The point of testing from the shell is that it removes the editor from the equation. If the curl call returns a model list and the editor still behaves as before, you have localised the fault to the client (the override string or the restart) rather than to the key or the network. That distinction decides whether the next hour goes into configuration or into credentials, and it takes about fifteen seconds to establish.

Own-key failures and what each one is actually telling you

Symptom	What is actually happening	How to confirm	Fix
Still billing the subscription after adding a key	The override was not saved, or was saved but not re-read, several versions only re-read it on a cold start.	Check your gateway usage log for a request you just made. Nothing there means the override did not take.	Save the override, then fully quit and relaunch rather than just closing the window.
404 on the messages path	A doubled /v1: the client appends the resource path itself, so a base URL that already ends in /v1 produces /v1/v1.	curl the same URL shape you typed. Whichever shape returns a model list is the shape the client needs.	Strip the trailing path so the URL ends at /v1.
401 with a key you just created	Truncation on paste, trailing whitespace, or a stale variable in a long-lived shell.	Print the first six characters of what the client holds (never log the whole key).	Paste into a plain text editor first to confirm the full string, then into the tool.
Works for one request, then 429	Your own per-model rate limit. The editor sends traffic faster than interactive use does.	Compare the error against a request you send by hand with curl.	Reduce concurrency. This is not a client bug and restarting will not change it.
Requests hang with no error	A proxy or firewall on the endpoint host, most often on corporate networks.	curl from the same machine. If curl hangs too, it is network-level.	Exclude the host from the proxy rather than unsetting it globally.
Tool calls fail silently	The endpoint does not fully implement tool calling, so the model answers in prose and never touches the repo.	Test tool use explicitly before relying on agent mode.	Pick a model that declares tool support, or drop to a non-agent workflow.

When this is the wrong move

Three responses that make a Cursor key problem worse

Situation	Why it breaks	Do this instead
You are about to regenerate the key again	Most failures on this page are not invalid keys. Regenerating invalidates every other working deployment while you check.	Confirm the key independently with curl before touching it.
You are about to keep retrying in the editor	Retries consume the same window that refused you, and the editor resends file context on every attempt.	Reproduce outside the editor, then change one variable at a time.
You plan to route every task to the flagship model	The editor resends context constantly, so per-request differences compound over hundreds of requests.	Split by task: cheap model for mechanical work, strong model for multi-file reasoning.

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.

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