Anthropic API Proxy for Gemini & OpenAI Models 🔄

Use Anthropic clients (like Claude Code) with Gemini or OpenAI backends. 🤝

A proxy server that lets you use Anthropic clients with Gemini or OpenAI models via LiteLLM. 🌉

Quick Start ⚡

Prerequisites

• OpenAI API key 🔑
• Google AI Studio (Gemini) API key (if using default provider) 🔑
• uv (recommended) or pip installed.

Setup 🛠️

1. Clone this repository:

   git clone https://github.com/1rgs/claude-code-openai.git
   cd claude-code-openai
   

2. Install dependencies: Using uv (recommended):

   uv venv # Create virtual environment (optional but recommended)
   uv pip install fastapi uvicorn litellm python-dotenv httpx # Install main packages
   

   Or using pip:

   python -m venv .venv
   source .venv/bin/activate # Or .\venv\Scripts\activate on Windows
   pip install fastapi uvicorn litellm python-dotenv httpx
   

3. Configure Environment Variables: Copy the example environment file:

   cp .env.example .env
   

   Edit .env and fill in your API keys and model configurations:

   • ANTHROPIC_API_KEY: (Optional) Needed only if proxying to Anthropic models.
   • OPENAI_API_KEY: Your OpenAI API key (Required if using OpenAI models as fallback or primary).
   • GEMINI_API_KEY: Your Google AI Studio (Gemini) API key (Required if using the default Gemini preference).
   • PREFERRED_PROVIDER (Optional): Set to google (default) or openai. This determines the primary backend for mapping haiku/sonnet.
   • BIG_MODEL (Optional): The model to map sonnet requests to. Defaults to gemini-1.5-pro-latest (if PREFERRED_PROVIDER=google and model is known) or gpt-4o.
   • SMALL_MODEL (Optional): The model to map haiku requests to. Defaults to gemini-1.5-flash-latest (if PREFERRED_PROVIDER=google and model is known) or gpt-4o-mini.

   Mapping Logic:

   • If PREFERRED_PROVIDER=google (default), haiku/sonnet map to SMALL_MODEL/BIG_MODEL prefixed with gemini/ if those models are in the server's known GEMINI_MODELS list.
   • Otherwise (if PREFERRED_PROVIDER=openai or the specified Google model isn't known), they map to SMALL_MODEL/BIG_MODEL prefixed with openai/.

4. Run the server: Using uv:

   uv run uvicorn server:app --host 0.0.0.0 --port 8082 --reload
   

   Or directly with uvicorn (if installed globally or in activated venv):

   uvicorn server:app --host 0.0.0.0 --port 8082 --reload
   

Using with Claude Code 🎮

1. Install Claude Code (if you haven't already):

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

2. Connect to your proxy:

   ANTHROPIC_BASE_URL=http://localhost:8082 claude
   

3. That's it! Your Claude Code client will now use the configured backend models (defaulting to Gemini) through the proxy. 🎯

Model Mapping 🗺️

The proxy automatically maps Claude models to either OpenAI or Gemini models based on the configured model:

Claude Model	Default Mapping	When BIG_MODEL/SMALL_MODEL is a Gemini model
haiku	openai/gpt-4o-mini	gemini/[model-name]
sonnet	openai/gpt-4o	gemini/[model-name]

Supported Models

OpenAI Models

The following OpenAI models are supported with automatic openai/ prefix handling:

• o3-mini
• o1
• o1-mini
• o1-pro
• gpt-4.5-preview
• gpt-4o
• gpt-4o-audio-preview
• chatgpt-4o-latest
• gpt-4o-mini
• gpt-4o-mini-audio-preview

Gemini Models

The following Gemini models are supported with automatic gemini/ prefix handling:

• gemini-2.5-pro-preview-03-25
• gemini-2.0-flash

Model Prefix Handling

The proxy automatically adds the appropriate prefix to model names:

• OpenAI models get the openai/ prefix
• Gemini models get the gemini/ prefix
• The BIG_MODEL and SMALL_MODEL will get the appropriate prefix based on whether they're in the OpenAI or Gemini model lists

For example:

• gpt-4o becomes openai/gpt-4o
• gemini-2.5-pro-preview-03-25 becomes gemini/gemini-2.5-pro-preview-03-25
• When BIG_MODEL is set to a Gemini model, Claude Sonnet will map to gemini/[model-name]

Customizing Model Mapping

You can customize which models are used via environment variables:

• BIG_MODEL: The model to use for Claude Sonnet models (default: "gpt-4o")
• SMALL_MODEL: The model to use for Claude Haiku models (default: "gpt-4o-mini")

Add these to your .env file to customize:

OPENAI_API_KEY=your-openai-key
# For OpenAI models (default)
BIG_MODEL=gpt-4o
SMALL_MODEL=gpt-4o-mini

# For Gemini models
# BIG_MODEL=gemini-2.5-pro-preview-03-25
# SMALL_MODEL=gemini-2.0-flash

Or set them directly when running the server:

# Using OpenAI models (with uv)
BIG_MODEL=gpt-4o SMALL_MODEL=gpt-4o-mini uv run uvicorn server:app --host 0.0.0.0 --port 8082

# Using Gemini models (with uv)
BIG_MODEL=gemini-2.5-pro-preview-03-25 SMALL_MODEL=gemini-2.0-flash uv run uvicorn server:app --host 0.0.0.0 --port 8082

# Mix and match (with uv)
BIG_MODEL=gemini-2.5-pro-preview-03-25 SMALL_MODEL=gpt-4o-mini uv run uvicorn server:app --host 0.0.0.0 --port 8082

How It Works 🧩

This proxy works by:

1. Receiving requests in Anthropic's API format 📥
2. Translating the requests to OpenAI format via LiteLLM 🔄
3. Sending the translated request to OpenAI 📤
4. Converting the response back to Anthropic format 🔄
5. Returning the formatted response to the client ✅

The proxy handles both streaming and non-streaming responses, maintaining compatibility with all Claude clients. 🌊

Contributing 🤝

Contributions are welcome! Please feel free to submit a Pull Request. 🎁