A 401 Narrows the Search, Not the Diagnosis

A 401 identifies an authentication boundary failure

An AI API returns 401, and the obvious diagnosis is a bad key. That is a useful hypothesis, not a complete explanation. The credential may be missing, expired, revoked, malformed, or intended for another service. A gateway may also reject the request before it reaches the model provider.

The standard meaning of 401 is that the request lacks valid authentication credentials for the target resource. It does not establish that your prompt, model choice, or account balance caused the failure. Follow the request outward, checking one boundary at a time.

First preserve the response without exposing credentials

Record the status, response body, timestamp, and any request identifier. Note the client and intended service. Preserve response headers when safe, especially authentication challenges and correlation identifiers, but redact secrets before sharing logs.

Read the error message alongside the status. A message about an absent credential suggests a different investigation from one describing a revoked key. Error formats can suggest where a response originated, but branding alone is not proof: intermediaries sometimes forward upstream errors unchanged.

Do not paste a complete API key into a support ticket. If a secret has already reached a public log or repository, revoke it and issue a replacement rather than merely hiding the visible copy.

Next confirm the credential belongs to the destination

Check that the destination and credential were issued by the same service. A direct provider key generally cannot authenticate to an independent relay, and a relay key generally cannot authenticate directly to the provider. Similar request formats do not make credentials interchangeable.

BestRelay is a quality-first relay covering Claude, GPT, Gemini, DeepSeek, Kimi, GLM, Qwen, Grok, and more. It forwards each request to the official model named in that request, without substitution. That routing commitment does not eliminate separate authentication boundaries between the client, relay, and provider.

Confirm the intended API base in the client without copying secrets into screenshots. An old destination paired with a newly issued key can produce a persistent 401 even when both settings look individually plausible.

Then inspect the credentials actually being transmitted

Check the running process, not just the settings you remember editing. A terminal session, background agent, or deployed worker may still hold an older credential. Multiple settings sources can also override one another.

Look for accidental whitespace, truncated values, and an authentication scheme that does not match the target API. Different interfaces may expect different headers or credential formats. Do not assume that every AI endpoint accepts the same authentication convention.

BestRelay works with Claude Code, Codex, Gemini CLI, and any OpenAI SDK. Compatibility still requires the appropriate destination, credential, and supported request interface. If the same account succeeds in one client but fails in another, compare their effective settings before rotating another key.

Separate authentication failures from neighboring account problems

A 403 ordinarily indicates refusal rather than a request for valid authentication, while 429 commonly signals rate limiting and sometimes quota exhaustion. Providers vary, however, so use their error details rather than treating those distinctions as universal implementation rules.

Inspect account status, project membership, model access, and spending restrictions when the response points there. Do not assume that adding funds repairs a 401. BestRelay bills pay-as-you-go using provider-reported token counts, with cache reads and writes priced separately. Members also earn referral commission when invited users top up; neither billing nor referral activity establishes credential validity.

Finally isolate one change before retrying once

Make a minimal request through the intended interface after correcting one suspected cause. Avoid changing the key, destination, model, and client simultaneously: a successful result would reveal little about the original failure.

If the 401 persists, ask support to trace the request identifier and identify the rejecting boundary. Share sanitized evidence and the checks already completed. Avoid automatic retry loops for unchanged authentication failures; repetition rarely repairs credentials, and recovered requests may incur charges.

Create a BestRelay account when you are ready. Keep relay and provider credentials distinct, and treat every 401 as a boundary to investigate rather than a verdict about the model.