Anthropic Proxy

A TypeScript-based proxy service that allows Anthropic/Claude API requests to be routed through an OpenAI compatible API to access alternative models.

Overview

Anthropic/Claude Proxy provides a compatibility layer between Anthropic/Claude and alternative models available through either e.g. OpenRouter or OpenAI compatible API URL. It dynamically selects models based on the requested Claude model name, mapping Opus/Sonnet to a configured "big model" and Haiku to a "small model".

Key features:

• Express.js web server exposing Anthropic/Claude compatible endpoints
• Format conversion between Anthropic/Claude API and OpenAI API requests/responses (see MAPPING for translation details)
• Support for both streaming and non-streaming responses
• Dynamic model selection based on requested Claude model
• Detailed request/response logging
• Token counting
• CLI interface with npm package distribution

Model: deepseek/deepseek-chat-v3-0324 on OpenRouter

Model: claude-sonnet-4 on Github Copilot

Installation

Global Installation

$ npm install -g anthropic-proxy-nextgen

Local Installation

$ npm install anthropic-proxy-nextgen

Usage

CLI Usage

Start the proxy server using the CLI:

$ npx anthropic-proxy-nextgen start \
  --port 8080 \
  --base-url=http://localhost:4000 \
  --big-model-name=github-copilot-claude-sonnet-4 \
  --small-model-name=github-copilot-claude-3.5-sonnet \
  --openai-api-key=sk-your-api-key \
  --log-level=DEBUG

or run with node:

$ node dist/cli.js start \
  --port 8080 \
  --base-url=http://localhost:4000 \
  --big-model-name=github-copilot-claude-sonnet-4 \
  --small-model-name=github-copilot-claude-3.5-sonnet \
  --openai-api-key=sk-your-api-key \
  --log-level=DEBUG

CLI Options

• --port, -p <port>: Port to listen on (default: 8080)
• --host, -h <host>: Host to bind to (default: 127.0.0.1)
• --base-url <url>: Base URL for the OpenAI-compatible API (required)
• --openai-api-key <key>: API key for the OpenAI-compatible service (required)
• --big-model-name <name>: Model name for Opus/Sonnet requests (default: github-copilot-claude-sonnet-4)
• --small-model-name <name>: Model name for Haiku requests (default: github-copilot-claude-3.5-sonnet)
• --referrer-url <url>: Referrer URL for requests (auto-generated if not provided)
• --log-level <level>: Log level - DEBUG, INFO, WARN, ERROR (default: INFO)
• --log-file <path>: Log file path for JSON logs
• --no-reload: Disable auto-reload in development

Environment Variables

You can also use a .env file for configuration:

HOST=127.0.0.1
PORT=8080
REFERRER_URL=http://localhost:8080/AnthropicProxy
BASE_URL=http://localhost:4000
OPENAI_API_KEY=sk-your-api-key
BIG_MODEL_NAME=github-copilot-claude-sonnet-4
SMALL_MODEL_NAME=github-copilot-claude-3.5-sonnet
LOG_LEVEL=DEBUG
LOG_FILE_PATH=./logs/anthropic-proxy-nextgen.jsonl

Programmatic Usage

import { startServer, createLogger, Config } from 'anthropic-proxy-nextgen';

const config: Config = {
  host: '127.0.0.1',
  port: 8080,
  baseUrl: 'http://localhost:4000',
  openaiApiKey: 'sk-your-api-key',
  bigModelName: 'github-copilot-claude-sonnet-4',
  smallModelName: 'github-copilot-claude-3.5-sonnet',
  referrerUrl: 'http://localhost:8080/AnthropicProxy',
  logLevel: 'INFO',
  reload: false,
  appName: 'AnthropicProxy',
  appVersion: '1.0.0',
};

const logger = createLogger(config);
await startServer(config, logger);

Development

Prerequisites

• Node.js 18+
• TypeScript 5+

Setup

# Clone the repository
$ git clone <repository-url>
$ cd AnthropicProxy

# Install dependencies
$ npm install

# Build the project
$ npm run build

# Run in development mode
$ npm run dev

# Run tests
$ npm test

# Lint and type check
$ npm run lint
$ npm run type-check

Build Commands

• npm run build: Compile TypeScript to JavaScript
• npm run dev: Run in development mode with auto-reload
• npm start: Start the compiled server
• npm test: Run tests
• npm run lint: Run ESLint
• npm run type-check: Run TypeScript type checking

API Endpoints

The proxy server exposes the following endpoints:

• POST /v1/messages: Create a message (main endpoint)
• POST /v1/messages/count_tokens: Count tokens for a request
• GET /: Health check endpoint

Using with Claude Code

# Set the base URL to point to your proxy
ANTHROPIC_BASE_URL=http://localhost:8080 claude

Configuration Examples

OpenRouter

$ npx anthropic-proxy-nextgen start \
  --base-url=https://openrouter.ai/api/v1 \
  --openai-api-key=sk-or-v1-your-openrouter-key \
  --big-model-name=anthropic/claude-3-opus \
  --small-model-name=anthropic/claude-3-haiku

GitHub Copilot

$ npx anthropic-proxy-nextgen start \
  --base-url=http://localhost:4000 \
  --openai-api-key=sk-your-github-copilot-key \
  --big-model-name=github-copilot-claude-sonnet-4 \
  --small-model-name=github-copilot-claude-3.5-sonnet

Local LLM

$ npx anthropic-proxy-nextgen start \
  --base-url=http://localhost:1234/v1 \
  --openai-api-key=not-needed \
  --big-model-name=local-large-model \
  --small-model-name=local-small-model

MCP

$ claude mcp add Context7 -- npx -y @upstash/context7-mcp
Added stdio MCP server Context7 with command: npx -y @upstash/context7-mcp to local config

$ claude mcp add atlassian -- npx -y mcp-remote https://mcp.atlassian.com/v1/sse
Added stdio MCP server atlassian with command: npx -y mcp-remote https://mcp.atlassian.com/v1/sse to local config

$ claude mcp add sequential-thinking -- npx -y @modelcontextprotocol/server-sequential-thinking
Added stdio MCP server sequential-thinking with command: npx -y @modelcontextprotocol/server-sequential-thinking to local config

$ claude mcp add sequential-thinking-tools -- npx -y mcp-sequentialthinking-tools
Added stdio MCP server sequential-thinking-tools with command: npx -y mcp-sequentialthinking-tools to local config

$ claude mcp add --transport http github https://api.githubcopilot.com/mcp/
Added HTTP MCP server github with URL: https://api.githubcopilot.com/mcp/ to local config

$ claude mcp list
Context7: npx -y @upstash/context7-mcp
sequential-thinking: npx -y @modelcontextprotocol/server-sequential-thinking
mcp-sequentialthinking-tools: npx -y mcp-sequentialthinking-tools
atlassian: npx -y mcp-remote https://mcp.atlassian.com/v1/sse
github: https://api.githubcopilot.com/mcp/ (HTTP)

"mcpServers": {
  "Context7": {
    "type": "stdio",
    "command": "npx",
    "args": [
      "-y",
      "@upstash/context7-mcp"
    ],
    "env": {}
  },
  "sequential-thinking": {
    "type": "stdio",
    "command": "npx",
    "args": [
      "-y",
      "@modelcontextprotocol/server-sequential-thinking"
    ],
    "env": {}
  },
  "mcp-sequentialthinking-tools": {
    "type": "stdio",
    "command": "npx",
    "args": [
      "-y",
      "mcp-sequentialthinking-tools"
    ]
  },
  "atlassian": {
    "type": "stdio",
    "command": "npx",
    "args": [
      "-y",
      "mcp-remote",
      "https://mcp.atlassian.com/v1/sse"
    ],
    "env": {}
  },
  "github": {
    "type": "http",
    "url": "https://api.githubcopilot.com/mcp/"
  }  
}

Architecture

This TypeScript implementation maintains the same core functionality as the Python version:

• Single-purpose Express server: Focused on API translation
• Model Selection Logic: Maps Claude models to configured target models
• Streaming Support: Full SSE streaming with proper content block handling
• Comprehensive Logging: Structured JSON logging with Winston
• Error Handling: Detailed error mapping between OpenAI and Anthropic formats
• Token Counting: Uses tiktoken for accurate token estimation

Migration from Python Version

The TypeScript version provides the same API and functionality as the Python FastAPI version. Key differences:

1. CLI Interface: Now provides a proper npm CLI package
2. Installation: Can be installed globally or locally via npm
3. Configuration: Same environment variables but also supports CLI arguments
4. Performance: Node.js async I/O for high concurrency
5. Dependencies: Uses Express.js instead of FastAPI, Winston instead of Python logging

REFERENCES

• Atlassian Remote MCP Server beta now available for desktop applications, https://community.atlassian.com/forums/Atlassian-Platform-articles/Atlassian-Remote-MCP-Server-beta-now-available-for-desktop/ba-p/3022084
• Using the Atlassian Remote MCP Server beta, https://community.atlassian.com/forums/Atlassian-Platform-articles/Using-the-Atlassian-Remote-MCP-Server-beta/ba-p/3005104

License

LICENSE