Anthropic

The anthropic provider speaks the native Anthropic Messages API. Use it for Claude models on Anthropic's own endpoint, or for any proxy that serves the same API shape.

model:
  provider: anthropic
  id: claude-sonnet-5

With no base_url, requests go to https://api.anthropic.com and the key is read from ANTHROPIC_API_KEY. Point api_key_env at a different env var if your key lives elsewhere; the mechanics are in Providers.

model:
  provider: anthropic
  id: claude-sonnet-5
  base_url: https://my-litellm-proxy.internal   # any Messages-API-compatible endpoint
  api_key_env: PROXY_API_KEY

Claude subscription auth

Instead of an API key, the provider accepts an OAuth token from a Claude Pro/Max subscription. Generate one with the Claude Code CLI:

claude setup-token

and export it as CLAUDE_CODE_OAUTH_TOKEN (no config change needed — the provider falls back to it when ANTHROPIC_API_KEY is unset). A token pasted into ANTHROPIC_API_KEY, or any env var named by api_key_env, also works: the provider recognizes the sk-ant-oat prefix and switches to Bearer auth with the oauth-2025-04-20 beta header automatically.

Disclaimer. Anthropic officially supports subscription usage through Claude Code and the Claude Agent SDK — not through direct Messages API calls. This token path works today, but Anthropic may restrict or reject non-Claude-Code use of subscription tokens at any time, and relying on it may be against their terms of service. Use it at your own risk, prefer an API key for anything production-critical, and expect requests to fail with an auth error if enforcement changes. Subscription tokens also draw from your plan's 5-hour/weekly usage windows rather than metered billing, so a busy agent competes with your own interactive usage.

One behavior worth knowing: this dialect caps output at 4096 tokens per call. The Messages API requires an explicit maximum and the framework deliberately has no config field for it, so we picked a fixed value. If a run needs longer single responses, put a rewriting proxy such as LiteLLM behind base_url; the reasoning is in what is deliberately not configurable.