antigravity-claude-proxy/CLAUDE.md

CLAUDE.md

This file provides guidance to Claude Code (claude.ai/code) when working with code in this repository.

Project Overview

Antigravity Claude Proxy is a Node.js proxy server that exposes an Anthropic-compatible API backed by Antigravity's Cloud Code service. It enables using Claude models (claude-sonnet-4-5-thinking, claude-opus-4-5-thinking) and Gemini models (gemini-3-flash, gemini-3-pro-low, gemini-3-pro-high) with Claude Code CLI.

The proxy translates requests from Anthropic Messages API format → Google Generative AI format → Antigravity Cloud Code API, then converts responses back to Anthropic format with full thinking/streaming support.

Commands

# Install dependencies
npm install

# Start server (runs on port 8080)
npm start

# Start with file watching for development
npm run dev

# Account management
npm run accounts         # Interactive account management
npm run accounts:add     # Add a new Google account via OAuth
npm run accounts:list    # List configured accounts
npm run accounts:verify  # Verify account tokens are valid

# Run all tests (server must be running on port 8080)
npm test

# Run 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

Architecture

Request Flow:

Claude Code CLI → Express Server (server.js) → CloudCode Client → Antigravity Cloud Code API

Key Modules:

• src/server.js: Express server exposing Anthropic-compatible endpoints (/v1/messages, /v1/models, /health, /account-limits)
• src/cloudcode-client.js: Makes requests to Antigravity Cloud Code API with retry/failover logic, handles both streaming and non-streaming
• src/format/: Format conversion module (Anthropic ↔ Google Generative AI)
  • index.js - Re-exports all converters
  • request-converter.js - Anthropic → Google request conversion
  • response-converter.js - Google → Anthropic response conversion
  • content-converter.js - Message content and role conversion
  • schema-sanitizer.js - JSON Schema cleaning for Gemini API compatibility (preserves constraints/enums as hints)
  • thinking-utils.js - Thinking block validation, filtering, reordering, and recovery logic
  • signature-cache.js - In-memory cache for Gemini thoughtSignatures
• src/account-manager.js: Multi-account pool with sticky selection, rate limit handling, and automatic cooldown
• src/oauth.js: Google OAuth implementation for adding accounts
• src/token-extractor.js: Extracts tokens from local Antigravity app installation (legacy single-account mode)
• src/constants.js: API endpoints, model mappings, OAuth config, and all configuration values
• src/errors.js: Custom error classes (RateLimitError, AuthError, ApiError, etc.) for structured error handling
• src/utils/helpers.js: Shared utility functions (formatDuration, sleep)

Multi-Account Load Balancing:

• Sticky account selection for prompt caching (stays on same account across turns)
• Automatic switch only when rate-limited for > 2 minutes
• Session ID derived from first user message hash for cache continuity
• Account state persisted to ~/.config/antigravity-proxy/accounts.json

Prompt Caching:

• Cache is organization-scoped (requires same account + session ID)
• Session ID is SHA256 hash of first user message content (stable across turns)
• cache_read_input_tokens returned in usage metadata when cache hits
• Token calculation: input_tokens = promptTokenCount - cachedContentTokenCount

Testing Notes

• Tests require the server to be running (npm start in separate terminal)
• Tests are CommonJS files (.cjs) that make HTTP requests to the local proxy
• Shared test utilities are in tests/helpers/http-client.cjs
• Test runner supports filtering: node tests/run-all.cjs <filter> to run matching tests

Code Organization

Constants: All configuration values are centralized in src/constants.js:

• API endpoints and headers
• Model mappings and model family detection (getModelFamily(), isThinkingModel())
• OAuth configuration
• Rate limit thresholds
• Thinking model settings

Model Family Handling:

• getModelFamily(model) returns 'claude' or 'gemini' based on model name
• Claude models use signature field on thinking blocks
• Gemini models use thoughtSignature field on functionCall parts (cached or sentinel value)
• When Claude Code strips thoughtSignature, the proxy tries to restore from cache, then falls back to skip_thought_signature_validator

Error Handling: Use custom error classes from src/errors.js:

• RateLimitError - 429/RESOURCE_EXHAUSTED errors
• AuthError - Authentication failures
• ApiError - Upstream API errors
• Helper functions: isRateLimitError(), isAuthError()

Utilities: Shared helpers in src/utils/helpers.js:

• formatDuration(ms) - Format milliseconds as "1h23m45s"
• sleep(ms) - Promise-based delay

Maintenance

When making significant changes to the codebase (new modules, refactoring, architectural changes), update this CLAUDE.md and the README.md file to keep documentation in sync.