local-openai2anthropic 0.3.9

A lightweight proxy server that converts Anthropic Messages API to OpenAI API

local-openai2anthropic

English | 中文

A lightweight proxy that lets applications built with Claude SDK talk to locally-hosted OpenAI-compatible LLMs.

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What Problem This Solves

Many local LLM tools (vLLM, SGLang, etc.) provide an OpenAI-compatible API. But if you've built your app using Anthropic's Claude SDK, you can't use them directly.

This proxy translates Claude SDK calls to OpenAI API format in real-time, enabling:

• Local LLM inference with Claude-based apps
• Offline development without cloud API costs
• Privacy-first AI - data never leaves your machine
• Seamless model switching between cloud and local
• Web Search tool - built-in Tavily web search for local models

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Supported Local Backends

Currently tested and supported:

Backend	Description	Status
vLLM	High-throughput LLM inference	✅ Fully supported
SGLang	Fast structured language model serving	✅ Fully supported

Other OpenAI-compatible backends may work but are not fully tested.

---

Quick Start

1. Install

pip install local-openai2anthropic

2. Configure Your LLM Backend (Optional)

Option A: Start a local LLM server

If you don't have an LLM server running, you can start one locally:

Example with vLLM:

vllm serve meta-llama/Llama-2-7b-chat-hf
# vLLM starts OpenAI-compatible API at http://localhost:8000/v1

Or with SGLang:

sglang launch --model-path meta-llama/Llama-2-7b-chat-hf --port 8000
# SGLang starts at http://localhost:8000/v1

Option B: Use an existing OpenAI-compatible API

If you already have a deployed OpenAI-compatible API (local or remote), you can use it directly. Just note the base URL for the next step.

Examples:

• Local vLLM/SGLang: http://localhost:8000/v1
• Remote API: https://api.example.com/v1

Note: If you're using Ollama, it natively supports the Anthropic API format, so you don't need this proxy. Just point your Claude SDK directly to http://localhost:11434/v1.

3. Start the Proxy (Recommended)

Run the following command to start the proxy in background mode:

oa2a start

First-time setup: If ~/.oa2a/config.toml doesn't exist, an interactive setup wizard will guide you through:

• Enter your OpenAI API Key (for the local LLM backend)
• Enter the base URL of your local LLM (e.g., http://localhost:8000/v1)
• Configure server host and port (optional)
• Set server API key for authentication (optional)

After configuration, the server starts at http://localhost:8080.

Daemon management commands:

oa2a logs               # Show last 50 lines of logs
oa2a logs -f            # Follow logs in real-time (Ctrl+C to exit)
oa2a status             # Check if server is running
oa2a stop               # Stop background server
oa2a restart            # Restart with same settings

Manual Configuration

You can also manually create/edit the config file at ~/.oa2a/config.toml:

# OA2A Configuration File
openai_api_key = "dummy"
openai_base_url = "http://localhost:8000/v1"
host = "0.0.0.0"
port = 8080

Option B: Run in foreground

oa2a                    # Run server in foreground (blocking)
# Press Ctrl+C to stop

4. Use in Your App

import anthropic

client = anthropic.Anthropic(
    base_url="http://localhost:8080",  # Point to proxy
    api_key="dummy-key",  # Not used
)

message = client.messages.create(
    model="meta-llama/Llama-2-7b-chat-hf",  # Your local model name
    max_tokens=1024,
    messages=[{"role": "user", "content": "Hello!"}],
)

print(message.content[0].text)

---

Using with Claude Code

You can configure Claude Code to use your local LLM through this proxy.

Configuration Steps

1. Edit Claude Code config file at ~/.claude/settings.json:

{
  "env": {
    "ANTHROPIC_BASE_URL": "http://localhost:8080",
    "ANTHROPIC_API_KEY": "dummy-key",
    "ANTHROPIC_MODEL": "meta-llama/Llama-2-7b-chat-hf",
    "ANTHROPIC_DEFAULT_SONNET_MODEL": "meta-llama/Llama-2-7b-chat-hf",
    "ANTHROPIC_DEFAULT_OPUS_MODEL": "meta-llama/Llama-2-7b-chat-hf",
    "ANTHROPIC_DEFAULT_HAIKU_MODEL": "meta-llama/Llama-2-7b-chat-hf",
    "ANTHROPIC_REASONING_MODEL": "meta-llama/Llama-2-7b-chat-hf"
  }
}

Variable	Description
ANTHROPIC_MODEL	General model setting
ANTHROPIC_DEFAULT_SONNET_MODEL	Default model for Sonnet mode (Claude Code default)
ANTHROPIC_DEFAULT_OPUS_MODEL	Default model for Opus mode
ANTHROPIC_DEFAULT_HAIKU_MODEL	Default model for Haiku mode
ANTHROPIC_REASONING_MODEL	Default model for reasoning tasks

Complete Workflow Example

Make sure ~/.claude/settings.json is configured as described above.

Terminal 1 - Start your local LLM:

vllm serve meta-llama/Llama-2-7b-chat-hf

Terminal 2 - Start the proxy (background mode):

# First run: interactive setup wizard will guide you
oa2a start

Terminal 3 - Launch Claude Code:

claude

Now Claude Code will use your local LLM instead of the cloud API.

To stop the proxy:

oa2a stop

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Features

• ✅ Streaming responses - Real-time token streaming via SSE
• ✅ Tool calling - Local LLM function calling support
• ✅ Vision models - Multi-modal input for vision-capable models
• ✅ Web Search - Built-in Tavily web search for local models
• ✅ Thinking mode - Supports reasoning/thinking model outputs

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Web Search 🔍

Enable web search for your local LLM using Tavily.

Setup:

1. Get a free API key at tavily.com

2. Add to your config (~/.oa2a/config.toml):

tavily_api_key = "tvly-your-api-key"

3. Use web_search_20250305 tool in your app - the proxy handles search automatically.

Options: tavily_max_results (default: 5), tavily_timeout (default: 30), websearch_max_uses (default: 5)

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Configuration

Config file: ~/.oa2a/config.toml (auto-created on first run)

Option	Required	Default	Description
openai_base_url	✅	-	Local LLM endpoint (e.g., http://localhost:8000/v1)
openai_api_key	✅	-	API key for local LLM
port	❌	8080	Proxy port
host	❌	0.0.0.0	Proxy host
api_key	❌	-	Auth key for this proxy
tavily_api_key	❌	-	Enable web search
log_level	❌	INFO	DEBUG, INFO, WARNING, ERROR

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Architecture

Your App (Claude SDK)
         │
         ▼
┌─────────────────────┐
│  local-openai2anthropic  │  ← This proxy
│  (Port 8080)        │
└─────────────────────┘
         │
         ▼
Your Local LLM Server
(vLLM / SGLang)
(OpenAI-compatible API)

---

Development

git clone https://github.com/dongfangzan/local-openai2anthropic.git
cd local-openai2anthropic
pip install -e ".[dev]"

pytest

License

Apache License 2.0