Overview

Claude Adapter is a lightweight proxy that converts Anthropic Messages API requests to OpenAI Chat Completions format, enabling you to use OpenAI-compatible APIs (like GPT-4, Local LLMs via vLLM, etc.) with Claude Code.

Input (Claude)

POST /v1/messages

Output (OpenAI)

POST /v1/chat/completions

# Installation

Prerequisites: Node.js 20.0.0 or higher.

bash
npm install -g claude-adapter

# Configuration

Run the tool for the first time to start the interactive configuration wizard.

bash
claude-adapter

CLI Options

Option	Description	Default
-p, --port	Port for proxy server	3080
-r, --reconfigure	Force reconfiguration	false

Model Mapping

You can map Claude model names to specific OpenAI deployments.

opus → gpt-5.2-codex
sonnet → gpt-5.2-mini
haiku → gpt-5.2-nano

# API Reference

You can use the adapter programmatically in your own Node.js applications.

typescript
import { createServer, AdapterConfig } from 'claude-adapter';

const config: AdapterConfig = {
  baseUrl: 'https://api.openai.com/v1',
  apiKey: process.env.OPENAI_API_KEY!,
  models: {
    opus: 'gpt-4-turbo',
    sonnet: 'gpt-3.5-turbo'
  }
};

const server = createServer(config);
await server.start(3080);

Troubleshooting

Port already in use

If port 3080 is taken, specify a custom port:

claude-adapter --port 3000

Claude Code not connecting

Verify ~/.claude/settings.json contains:


{
  "env": {
    "ANTHROPIC_BASE_URL": "http://localhost:3080"
  }
}