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Claude Code

Use Onefast API in Claude Code, Anthropic's official command-line coding assistant.

1. Install

Shell

npm install -g @anthropic-ai/claude-code@latest

Requires Node.js 18 or later.

2. Configure

Edit (or create) ~/.claude/settings.json. On Windows the path is %USERPROFILE%\.claude\settings.json:

~/.claude/settings.json

{
  "env": {
    "ANTHROPIC_BASE_URL": "https://api.onefast.ai",
    "ANTHROPIC_AUTH_TOKEN": "sk-xxx",
    "CLAUDE_CODE_ATTRIBUTION_HEADER": "0",
    "CLAUDE_CODE_DISABLE_NONESSENTIAL_TRAFFIC": "1"
  }
}
  • Set ANTHROPIC_BASE_URL to the root URL — without /v1.
  • Set ANTHROPIC_AUTH_TOKEN to your key. We recommend creating a dedicated key for Claude Code with Claude groups selected.

You can also configure it temporarily with environment variables:

macOS / Linux

export ANTHROPIC_BASE_URL="https://api.onefast.ai"
export ANTHROPIC_AUTH_TOKEN="sk-xxx"
claude

Windows PowerShell

$env:ANTHROPIC_BASE_URL = "https://api.onefast.ai"
$env:ANTHROPIC_AUTH_TOKEN = "sk-xxx"
claude

3. Verify

Shell

claude -p "Introduce yourself in one sentence."

If you get a normal reply, you're set. In the interactive UI, use /model to switch models (e.g. claude-opus-4-8, claude-sonnet-4-6).

Troubleshooting

It still asks me to log in / isn't using my key

If you have ever logged in to an Anthropic account (Claude Pro/Max) on this machine, the locally saved login credentials take precedence over ANTHROPIC_AUTH_TOKEN. Run /logout in Claude Code and try again, or give it a separate config directory:

Shell

export CLAUDE_CONFIG_DIR="$HOME/.claude-api"

On macOS, also check whether a leftover CLAUDE_CODE_OAUTH_TOKEN environment variable exists in your terminal; if so, run unset CLAUDE_CODE_OAUTH_TOKEN.

401 / 403 errors

  • 401: the key is wrong or deleted — check ANTHROPIC_AUTH_TOKEN.
  • 403 has no access to model: the key has a model allowlist; add the Claude models to it.
  • See Errors for more.

Long tasks disconnect midway

Claude Code can go a long time without output while it thinks. This is normal; the gateway keeps the connection open for up to 10 minutes. If you get disconnected often, check the idle timeout of your local proxy or corporate network.