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 Google provider) 🔑
• uv installed.

Setup 🛠️

1. Clone this repository:

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

2. Install uv (if you haven't already):

   curl -LsSf https://astral.sh/uv/install.sh | sh

   (uv will handle dependencies based on pyproject.toml when you run the server)

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 the default OpenAI preference or as fallback).
   • GEMINI_API_KEY: Your Google AI Studio (Gemini) API key (Required if PREFERRED_PROVIDER=google).
   • PREFERRED_PROVIDER (Optional): Set to openai (default) or google. This determines the primary backend for mapping haiku/sonnet.
   • BIG_MODEL (Optional): The model to map sonnet requests to. Defaults to gpt-4.1 (if PREFERRED_PROVIDER=openai) or gemini-2.5-pro-preview-03-25.
   • SMALL_MODEL (Optional): The model to map haiku requests to. Defaults to gpt-4.1-mini (if PREFERRED_PROVIDER=openai) or gemini-2.0-flash.

   Mapping Logic:

   • If PREFERRED_PROVIDER=openai (default), haiku/sonnet map to SMALL_MODEL/BIG_MODEL prefixed with openai/.
   • If PREFERRED_PROVIDER=google, haiku/sonnet map to SMALL_MODEL/BIG_MODEL prefixed with gemini/ if those models are in the server's known GEMINI_MODELS list (otherwise falls back to OpenAI mapping).

4. Run the server:

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

   (--reload is optional, for development)

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:

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
• gpt-4.1
• gpt-4.1-mini

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

Control the mapping using environment variables in your .env file or directly:

Example 1: Default (Use OpenAI)
No changes needed in .env beyond API keys, or ensure:

OPENAI_API_KEY="your-openai-key"
GEMINI_API_KEY="your-google-key" # Needed if PREFERRED_PROVIDER=google
# PREFERRED_PROVIDER="openai" # Optional, it's the default
# BIG_MODEL="gpt-4.1" # Optional, it's the default
# SMALL_MODEL="gpt-4.1-mini" # Optional, it's the default

Example 2: Prefer Google

GEMINI_API_KEY="your-google-key"
OPENAI_API_KEY="your-openai-key" # Needed for fallback
PREFERRED_PROVIDER="google"
# BIG_MODEL="gemini-2.5-pro-preview-03-25" # Optional, it's the default for Google pref
# SMALL_MODEL="gemini-2.0-flash" # Optional, it's the default for Google pref

Example 3: Use Specific OpenAI Models

OPENAI_API_KEY="your-openai-key"
GEMINI_API_KEY="your-google-key"
PREFERRED_PROVIDER="openai"
BIG_MODEL="gpt-4o" # Example specific model
SMALL_MODEL="gpt-4o-mini" # Example specific model

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. 🎁