Claude Code 401 and 403 Errors: Authentication Fixes That Work

A login page can say you are signed in while your terminal still refuses every request. That is confusing until you separate three questions: which server received the request, which credential it received, and what that credential is allowed to do. This guide uses those questions to narrow down 401 and 403 errors without randomly replacing your whole setup.

An identity problem and an access problem need different fixes

A useful starting model is that authentication establishes who is calling, while authorization establishes what that caller may do. In Anthropic's API terminology, 401 identifies an authentication problem and 403 identifies insufficient permission for a resource. A proxy may return its own rejection before the request reaches the model service, so always read the response body as well.

Picture an office building. The first failure resembles a badge reader that cannot accept your badge. The second resembles an accepted badge that does not open this particular room. Buying another badge or tapping it repeatedly is not a systematic way to diagnose either problem. You need to identify the issuing organization and the door you are trying to open.

Step 1: establish where the request went

Check the configured endpoint in the environment and application settings used by the failing client. Compare its hostname with the service that issued your credential. A Kintio key belongs with the Kintio endpoint; a key issued elsewhere is not interchangeable merely because two APIs use a similar JSON format.

Make a small troubleshooting note with the endpoint hostname, shell type, installed client version and time of failure. Include whether you launched from a terminal, editor or remote session. Those details help identify a different configuration scope without asking you to share a secret.

claude --version
# Bash: show only the routing setting
printf '%s\n' "${ANTHROPIC_BASE_URL:-not set in this shell}"

Step 2: distinguish browser sign-in from API-key access

Claude Code supports more than one access method. A successful browser login does not prove that a separately configured API key is valid. Likewise, a working key-based integration does not establish that your subscription sign-in is configured correctly. The official authentication guide explains the available account paths.

Choose the route you intend to use, then investigate that route. If you intend to use account sign-in, inspect whether an older key or gateway configuration remains in the launch environment. If you intend to use a provider key, check the provider dashboard for its active state and assigned scope. Follow the provider's authentication instructions rather than combining methods during diagnosis.

Avoid deleting all credential files as a first step. That can remove working access for other projects and leave you with less evidence. Record the current configuration locations and change one source at a time.

Step 3: inspect the credential's shape without revealing it

Copy-and-paste mistakes are common: leading spaces, an accidental newline, quotation marks copied as part of the value, or a placeholder never replaced. Check the original secret source privately. A presence check is useful, but a value being present does not make it correct.

If a key was revoked, expired or replaced, load the current one using your provider's normal process. If it was exposed in a public issue or repository, revoke it even if it still works. Do not post its first or last characters as proof of validity when a local dashboard can establish that fact.

When a team supplies credentials, ask which workspace and resource the key should access. The important question is not 'does anyone have a working key?' but 'does this credential have the intended permissions on this route?' That avoids solving an access problem by copying a colleague's secret.

Step 4: for a 403, check the exact denied resource

A request can fail for one model or endpoint while another works. If you have a known permitted model, use it for a small control test. Keep the endpoint and credential unchanged. A success on the control request narrows the investigation toward permissions or support for the original resource.

If every request is rejected with an HTML page, check whether a network gateway or web security rule generated that page. A browser-facing block page and a structured model API error are different clues. Capture the content type, request ID if present, and the hostname. An administrator can use those details to locate the rejecting layer.

Changing application file permissions or running the terminal as administrator does not normally grant remote model access. Local permissions and a remote service's access controls are different systems. Only change local privileges when the error actually identifies a local operation that requires them.

Step 5: run one controlled verification

After making a correction, start a fresh client from the intended shell and ask a small question. Record whether the status changed, not just whether the original wording disappeared. A transition from 401 to a model-not-found error suggests authentication may now be accepted but model selection still needs correction.

Once basic access works, test a harmless coding task in a disposable repository. This confirms that the interactive tool workflow works through the same route. An answer to a text question is not evidence that every agent feature is supported.

If the issue persists, stop changing unrelated settings. Send support a short, redacted report: expected route, credential type without its value, exact error text, timestamp, client version, and the outcome of the small control request. That report is far more actionable than 'login broken'.

Prevent the next authentication mystery

Maintain a short setup note for each environment: laptop shell, editor, WSL distribution and CI runner. Include the source of credentials and where to rotate them, without embedding the credentials. After rotation, verify each environment rather than assuming all running processes reload a secret together.

When evaluating a gateway such as Kintio, document its endpoint and authentication method as a pair. This article is published by Kintio; using a gateway can change how access is managed, but it does not make authorization checks disappear. Choose the route that fits your workflow and keep its configuration explicit.

Frequently asked questions

Does a 403 mean my key is definitely valid?

Treat it as an access clue, not a universal guarantee. Proxies and security layers can generate their own responses. Read the body and identify the rejecting service.

Should I reinstall Claude Code?

First check the route, credential source and permissions. Reinstalling the executable may leave those settings unchanged, so it often does not address the actual cause.

What can I share with support?

Share redacted error text, timestamps, request IDs and a minimal description of the failing operation. Do not share API keys, cookies or bearer tokens.

Related guides

• Understand environment variables and launch scopes
• Set up a custom endpoint

Last updated: 2026-10-10