Claude Code with a custom endpoint

Claude Code talks to the Anthropic Messages API, which 666 AI supports at /v1/messages. We installed Claude Code and ran it against our live API, including tool calls, before writing this page.

Replace YOUR-ENDPOINT with the endpoint shown on your API Key page after you sign up, and YOUR-KEY with your key. One key works for every model on 666 AI — Claude, GPT, Gemini, DeepSeek, Qwen and 200+ more.

1. Set the environment variables

# macOS / Linux (bash / zsh)
export ANTHROPIC_BASE_URL="https://YOUR-ENDPOINT"        # no /v1
export ANTHROPIC_AUTH_TOKEN="YOUR-KEY"
export ANTHROPIC_MODEL="anthropic/claude-sonnet-5.5"
export ANTHROPIC_DEFAULT_HAIKU_MODEL="anthropic/claude-haiku-5.5"
claude

2. Or put them in settings.json

// ~/.claude/settings.json   (Windows: %USERPROFILE%\.claude\settings.json)
{
  "env": {
    "ANTHROPIC_BASE_URL": "https://YOUR-ENDPOINT",
    "ANTHROPIC_AUTH_TOKEN": "YOUR-KEY",
    "ANTHROPIC_MODEL": "anthropic/claude-sonnet-5.5",
    "ANTHROPIC_DEFAULT_HAIKU_MODEL": "anthropic/claude-haiku-5.5"
  }
}

Use your user settings file. Don't put keys in a project's .claude/settings.json — that file is usually committed to git.

3. Check it

claude -p "Reply with exactly the word OK."

In an interactive session, /status shows the base URL and which variable your token came from.

Which models work

Use Claude models: anthropic/claude-sonnet-5.5 (recommended for coding), anthropic/claude-opus-5.5, anthropic/claude-haiku-5.5. Anthropic does not support running Claude Code on non-Claude models through gateways, so don't point it at GPT or Gemini.

In our test Sonnet 5.5 ran shell tools first time; the small Haiku model sometimes needed a retry on its first tool call — use Sonnet for agentic work.

If you get a 400 error

  1. context_management or Extra inputs are not permitted: set CLAUDE_CODE_DISABLE_EXPERIMENTAL_BETAS=1.
  2. Context-length errors in long sessions: set CLAUDE_CODE_AUTO_COMPACT_WINDOW and CLAUDE_CODE_MAX_OUTPUT_TOKENS to the model's real limits.
  3. 401: the key is wrong. ANTHROPIC_BASE_URL goes in without /v1.

FAQ

Do I need an Anthropic account?

No. Your 666 AI key is enough; usage is billed per token from your 666 AI balance.

ANTHROPIC_AUTH_TOKEN or ANTHROPIC_API_KEY?

Either works with 666 AI. AUTH_TOKEN sends a Bearer header and avoids the one-time key confirmation prompt.

Does the VS Code extension work too?

Yes — set the same variables in the extension's environment settings (claudeCode.environmentVariables).

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