Antigravity Claude Proxy

A proxy server that exposes an Anthropic-compatible API backed by Antigravity's Cloud Code, letting you use Claude models like claude-sonnet-4-5 with any Anthropic client including Claude Code CLI.

How It Works

┌──────────────────┐     ┌─────────────────────┐     ┌────────────────────────────┐
│   Claude Code    │────▶│  This Proxy Server  │────▶│  Antigravity Cloud Code    │
│   (Anthropic     │     │  (Anthropic → Google│     │  (daily-cloudcode-pa.      │
│    API format)   │     │   Generative AI)    │     │   sandbox.googleapis.com)  │
└──────────────────┘     └─────────────────────┘     └────────────────────────────┘

1. Receives requests in Anthropic Messages API format
2. Extracts OAuth token from Antigravity's local database
3. Transforms to Google Generative AI format with Cloud Code wrapping
4. Sends to Antigravity's Cloud Code API (v1internal:streamGenerateContent)
5. Converts responses back to Anthropic format

Prerequisites

• Antigravity installed and running (you must be logged in)
• Node.js 18 or later

Quick Start

1. Install Dependencies

npm install

2. Start the Proxy Server

npm start

The server runs on http://localhost:8080 by default.

3. Test It

# Health check
curl http://localhost:8080/health

# Simple message (non-streaming)
curl http://localhost:8080/v1/messages \
  -H "Content-Type: application/json" \
  -d '{
    "model": "claude-sonnet-4-5",
    "messages": [{"role": "user", "content": "Say hello!"}],
    "max_tokens": 100
  }'

# Streaming
curl http://localhost:8080/v1/messages \
  -H "Content-Type: application/json" \
  -d '{
    "model": "claude-sonnet-4-5",
    "messages": [{"role": "user", "content": "Say hello!"}],
    "max_tokens": 100,
    "stream": true
  }'

Using with Claude Code CLI

Configure Claude Code to use this proxy:

# Set the API base URL
export ANTHROPIC_BASE_URL=http://localhost:8080

# Use any API key (it's not actually used - auth comes from Antigravity)
export ANTHROPIC_API_KEY=dummy-key

# Run Claude Code
claude

Or in your Claude Code config:

{
  "apiBaseUrl": "http://localhost:8080",
  "apiKey": "dummy-key"
}

Available Models

Model ID	Description
claude-sonnet-4-5	Claude Sonnet 4.5 via Antigravity
claude-sonnet-4-5-thinking	Claude Sonnet 4.5 with extended thinking
claude-opus-4-5-thinking	Claude Opus 4.5 with extended thinking

You can also use standard Anthropic model names - they'll be automatically mapped:

• claude-3-5-sonnet-20241022 → claude-sonnet-4-5
• claude-3-opus-20240229 → claude-opus-4-5-thinking

API Endpoints

Endpoint	Method	Description
/health	GET	Health check and token status
/v1/messages	POST	Anthropic Messages API
/v1/models	GET	List available models
/refresh-token	POST	Force token refresh

Files

src/
├── index.js            # Entry point
├── server.js           # Express server with Anthropic API endpoints
├── cloudcode-client.js # Cloud Code API client with proper wrapping
├── format-converter.js # Anthropic ↔ Google format conversion
├── constants.js        # Endpoints, headers, model mappings
└── token-extractor.js  # Extracts OAuth token from Antigravity

Troubleshooting

"Could not extract token from Antigravity"

Make sure:

1. Antigravity app is running
2. You're logged in to Antigravity

401 Authentication Errors

The token might have expired. Try:

curl -X POST http://localhost:8080/refresh-token

Rate Limiting (429)

Antigravity enforces rate limits on Cloud Code requests. Wait and retry, or switch to a different model.

Credits

Based on insights from:

• opencode-antigravity-auth - Antigravity OAuth plugin for OpenCode
• claude-code-proxy - Anthropic API proxy using LiteLLM

License

MIT