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 🛠️

Clone this repository:

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

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)
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).

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 🎮

Install Claude Code (if you haven't already):
```
npm install -g @anthropic-ai/claude-code
```

Connect to your proxy:

ANTHROPIC_BASE_URL=http://localhost:8082 claude

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
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:

Receiving requests in Anthropic's API format 📥
Translating the requests to OpenAI format via LiteLLM 🔄
Sending the translated request to OpenAI 📤
Converting the response back to Anthropic format 🔄
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. 🎁

johnowennixon/claude-code-proxy

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