Antigravity Claude Proxy

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)  │
└──────────────────┘     └─────────────────────┘     └────────────────────────────┘

1. Receives requests in Anthropic Messages API format
2. Uses OAuth tokens from added Google accounts (or Antigravity's local database)
3. Transforms to Google Generative AI format with Cloud Code wrapping
4. Sends to Antigravity's Cloud Code API
5. 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

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Quick Start

1. Install Dependencies

npm install

2. 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:

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
npm run accounts:list

# Verify accounts are working
npm run accounts:verify

# Interactive account management
npm run accounts

3. Start the Proxy Server

npm start

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

4. 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"

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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
npm start

# In another terminal, run Claude Code
claude

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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

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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

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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:

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

Or add accounts via OAuth instead: npm run accounts:add

401 Authentication Errors

The token might have expired. Try:

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

Or re-authenticate the account:

npm run 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:

npm run accounts
# Choose "Re-authenticate" for the invalid account

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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.

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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.

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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

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License

MIT

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