Claude Code API proxy Base URL setup guide

Configure Claude Code with an API proxy using ANTHROPIC_BASE_URL, ANTHROPIC_AUTH_TOKEN, and ANTHROPIC_API_KEY.

Minimal setup

When connecting Claude Code to a proxy, first check whether the provider offers an Anthropic-compatible API. The most common setup is:

export ANTHROPIC_BASE_URL="https://your-proxy.example"
export ANTHROPIC_AUTH_TOKEN="your proxy API key"
claude

ANTHROPIC_BASE_URL routes requests to the proxy or gateway. ANTHROPIC_AUTH_TOKEN is sent as the Bearer token.

If you are comparing providers before configuring Claude Code, start with the Claude API Proxy Providers page. For a broader list of Anthropic-compatible, OpenAI-compatible, and multi-model providers, use the AI API Directory.

API key path

If the provider gives you an Anthropic-style API key, it may ask you to configure:

export ANTHROPIC_API_KEY="sk-..."
claude

Note: after ANTHROPIC_API_KEY is set, Claude Code uses that API key instead of the quota from a Claude Pro, Max, or Team subscription login. When testing a proxy, open a fresh terminal window and set the variables only in that window.

Common errors

  • 401: wrong key, wrong header type, or the provider expects ANTHROPIC_AUTH_TOKEN instead of ANTHROPIC_API_KEY.
  • 404: wrong Base URL path. Pay close attention to whether the provider requires /v1.
  • model not found: the model name is not available from the provider, or you need a custom model option.
  • MCP search issues: with a non-official Base URL, Claude Code may change MCP tool search behavior. Confirm whether the provider forwards the required capabilities fully.

Recommendation

Start with a clean terminal and a temporary configuration. After you confirm the setup works, move it into your shell profile, project scripts, or switching tool. Do not change global configuration first, or debugging becomes much harder: you will not know whether the problem is the account, environment variables, or provider API.

Claude Code Base URL API Key

Related errors

Claude Code / Codex 503 No available accounts Do not rotate keys first. This error usually points to an unavailable account pool, provider, group, or model route. Test a minimal request, confirm the model and group, then decide whether to wait, reduce context, change model, or switch provider. Error 401 Unauthorized for AI API proxies A 401 is an authentication failure. Check which key is loaded, which Base URL receives the request, whether the header format is correct, and whether the key is still active for that provider. Error 429 Too Many Requests for AI API proxies Error: exceeded retry limit, last status: 429 Too Many Requests, request id: <request-id>. With an AI API proxy, repeated 429s usually mean the upstream account pool is rate limited, cooling down, or out of usable quota. Ask the provider to switch account, route, or model first.