A proxy server that exposes an Anthropic-compatible API backed by Antigravity's Cloud Code, letting you use Claude models like sonnet and opus with 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)  │
└──────────────────┘     └─────────────────────┘     └────────────────────────────┘

Receives requests in Anthropic Messages API format
Uses OAuth tokens from added Google accounts (or Antigravity's local database)
Transforms to Google Generative AI format with Cloud Code wrapping
Sends to Antigravity's Cloud Code API
Converts responses back to Anthropic format with full thinking/streaming support

Prerequisites

Node.js 18 or later
Antigravity installed (for single-account mode) OR Google account(s) for multi-account mode

Installation

Option 1: npm (Recommended)

# Run directly with npx (no install needed)
npx antigravity-claude-proxy start

# Or install globally
npm install -g antigravity-claude-proxy
antigravity-claude-proxy start

Option 2: Clone Repository

git clone https://github.com/badri-s2001/antigravity-claude-proxy.git
cd antigravity-claude-proxy
npm install
npm start

Quick Start

1. Add Account(s)

You have two options:

Option A: Use Antigravity (Single Account)

If you have Antigravity installed and logged in, the proxy will automatically extract your token. No additional setup needed.

Option B: Add Google Accounts via OAuth (Recommended for Multi-Account)

Add one or more Google accounts for load balancing:

# If installed via npm
antigravity-claude-proxy accounts add

# If using npx
npx antigravity-claude-proxy accounts add

# If cloned locally
npm run accounts:add

This opens your browser for Google OAuth. Sign in and authorize access. Repeat for multiple accounts.

Manage accounts:

# List all accounts
antigravity-claude-proxy accounts list

# Verify accounts are working
antigravity-claude-proxy accounts verify

# Interactive account management
antigravity-claude-proxy accounts

2. Start the Proxy Server

# If installed via npm
antigravity-claude-proxy start

# If using npx
npx antigravity-claude-proxy start

# If cloned locally
npm start

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

3. Verify It's Working

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

# Check account status and quota limits
curl "http://localhost:8080/account-limits?format=table"

Using with Claude Code CLI

Configure Claude Code

Create or edit the Claude Code settings file:

macOS: ~/.claude/settings.json Linux: ~/.claude/settings.json Windows: %USERPROFILE%\.claude\settings.json

Add this configuration:

{
  "env": {
    "ANTHROPIC_AUTH_TOKEN": "test",
    "ANTHROPIC_BASE_URL": "http://localhost:8080",
    "ANTHROPIC_MODEL": "claude-opus-4-5-thinking",
    "ANTHROPIC_DEFAULT_OPUS_MODEL": "claude-opus-4-5-thinking",
    "ANTHROPIC_DEFAULT_SONNET_MODEL": "claude-sonnet-4-5-thinking",
    "ANTHROPIC_DEFAULT_HAIKU_MODEL": "claude-sonnet-4-5",
    "CLAUDE_CODE_SUBAGENT_MODEL": "claude-opus-4-5-thinking"
  }
}

Run Claude Code

# Make sure the proxy is running first
antigravity-claude-proxy start

# In another terminal, run Claude Code
claude

Available Models

Model ID	Description
`claude-sonnet-4-5-thinking`	Claude Sonnet 4.5 with extended thinking
`claude-opus-4-5-thinking`	Claude Opus 4.5 with extended thinking
`claude-sonnet-4-5`	Claude Sonnet 4.5 without thinking

Standard Anthropic model names are automatically mapped:

claude-sonnet-4-5-20250514 → claude-sonnet-4-5-thinking
claude-opus-4-5-20250514 → claude-opus-4-5-thinking

Multi-Account Load Balancing

When you add multiple accounts, the proxy automatically:

Sticky account selection: Stays on the same account to maximize prompt cache hits
Smart rate limit handling: Waits for short rate limits (≤2 min), switches accounts for longer ones
Automatic cooldown: Rate-limited accounts become available after reset time expires
Invalid account detection: Accounts needing re-authentication are marked and skipped
Prompt caching support: Stable session IDs enable cache hits across conversation turns

Check account status anytime:

curl "http://localhost:8080/account-limits?format=table"

API Endpoints

Endpoint	Method	Description
`/health`	GET	Health check
`/account-limits`	GET	Account status and quota limits (add `?format=table` for ASCII table)
`/v1/messages`	POST	Anthropic Messages API
`/v1/models`	GET	List available models
`/refresh-token`	POST	Force token refresh

Testing

Run the test suite (requires server running):

# Start server in one terminal
npm start

# Run tests in another terminal
npm test

Individual tests:

npm run test:signatures    # Thinking signatures
npm run test:multiturn     # Multi-turn with tools
npm run test:streaming     # Streaming SSE events
npm run test:interleaved   # Interleaved thinking
npm run test:images        # Image processing
npm run test:caching       # Prompt caching

Troubleshooting

"Could not extract token from Antigravity"

If using single-account mode with Antigravity:

Make sure Antigravity app is installed and running
Ensure you're logged in to Antigravity

Or add accounts via OAuth instead: antigravity-claude-proxy accounts add

401 Authentication Errors

The token might have expired. Try:

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

Or re-authenticate the account:

antigravity-claude-proxy accounts

Rate Limiting (429)

With multiple accounts, the proxy automatically switches to the next available account. With a single account, you'll need to wait for the rate limit to reset.

Account Shows as "Invalid"

Re-authenticate the account:

antigravity-claude-proxy accounts
# Choose "Re-authenticate" for the invalid account

Safety, Usage, and Risk Notices

Intended Use

Personal / internal development only
Respect internal quotas and data handling policies
Not for production services or bypassing intended limits

Not Suitable For

Production application traffic
High-volume automated extraction
Any use that violates Acceptable Use Policies

Warning (Assumption of Risk)

By using this software, you acknowledge and accept the following:

Terms of Service risk: This approach may violate the Terms of Service of AI model providers (Anthropic, Google, etc.). You are solely responsible for ensuring compliance with all applicable terms and policies.
Account risk: Providers may detect this usage pattern and take punitive action, including suspension, permanent ban, or loss of access to paid subscriptions.
No guarantees: Providers may change APIs, authentication, or policies at any time, which can break this method without notice.
Assumption of risk: You assume all legal, financial, and technical risks. The authors and contributors of this project bear no responsibility for any consequences arising from your use.

Use at your own risk. Proceed only if you understand and accept these risks.

Legal

Not affiliated with Google or Anthropic. This is an independent open-source project and is not endorsed by, sponsored by, or affiliated with Google LLC or Anthropic PBC.
"Antigravity", "Gemini", "Google Cloud", and "Google" are trademarks of Google LLC.
"Claude" and "Anthropic" are trademarks of Anthropic PBC.
Software is provided "as is", without warranty. You are responsible for complying with all applicable Terms of Service and Acceptable Use Policies.

Credits

This project is based on insights and code from:

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

License

MIT

README.md

Antigravity Claude Proxy