Claude Code Fallback

Automatically switch from your Claude subscription to API billing when you hit usage limits, keeping your coding session uninterrupted.

Note (December 2025): Claude Code now has built-in extra-usage support. This tool remains useful if you want:

• Background monitoring with OS notifications before you're blocked
• Auto-restart mode that switches automatically without any prompts
• Multi-terminal awareness (monitor runs independently, works in tmux/ssh)

If the built-in extra-usage feature meets your needs, you may not need this tool.

Why This Exists

Claude Code usage is shared with your web Claude.ai usage and resets every 5 hours. When you hit these limits during an active coding session, you're forced to either wait or manually switch to API billing. This tool automates that transition so you never lose momentum.

How It Works

A lightweight background monitor watches Claude Code's JSONL logs for usage limit errors:

1. You run Claude Code normally (no wrapper needed)
2. Background monitor detects when you've hit subscription limits
3. You receive a notification: "Usage limit reached! Run 'claude-api' to switch"
4. Exit Claude Code and run claude-api to restart with API billing
5. Continue working seamlessly in the same directory
6. Run claude-sub to switch back to subscription mode

Features

• Log-Based Detection: Monitors JSONL logs for usage limit errors
• Simple Shell Functions: Switch modes with claude-api and claude-sub commands
• Native Notifications: OS-level alerts when limits are detected
• Directory Preservation: Automatically restarts Claude in your working directory
• No Process Wrapping: Claude Code runs normally, no PTY manipulation
• Robust Daemon Mode: Background monitor with proper signal handling

Quick Start

1. Install

pip install claude-code-fallback

Or with uv:

uv pip install claude-code-fallback

2. Set Your API Key

Add to your ~/.zshrc or ~/.bashrc:

export CLAUDE_FALLBACK_API_KEY='sk-ant-api03-...'

Get your API key from console.anthropic.com

3. Install Shell Functions

claude-fallback install
source ~/.zshrc  # or ~/.bashrc

4. Start the Monitor

# Run in background (recommended)
claude-fallback start --daemon

# Or run in foreground
claude-fallback start

5. Use Claude Normally

claude

When you hit limits, you'll get a notification. Exit Claude and run:

claude-api    # Switch to API mode
claude-sub    # Switch back to subscription

Commands

CLI Commands

Command	Description
claude-fallback install	Install shell functions
claude-fallback start	Start monitor (foreground)
claude-fallback start --daemon	Start monitor (background)
claude-fallback stop	Stop background monitor
claude-fallback status	Show current status
claude-fallback clear	Clear limit detected state
claude-fallback help	Show help

Shell Functions

Function	Description
claude-api	Switch to API billing and start Claude
claude-sub	Switch to subscription and start Claude
claude-mode	Show current mode

Configuration

The tool uses environment variables (recommended) or a config file:

Environment Variables

# Required: Your Anthropic API key
export CLAUDE_FALLBACK_API_KEY='sk-ant-api03-...'

# Optional: Enable auto-restart (kills Claude and restarts in API mode)
export CLAUDE_FALLBACK_AUTO_RESTART=1

Config File (Alternative)

Create config.json in the project directory:

{
  "api_key": "sk-ant-api03-...",
  "auto_restart": true
}

Options

Option	Description
api_key	Your Anthropic API key (required)
auto_restart	When true, automatically kills Claude and restarts in API mode when limits hit. Your current conversation will end, but a new session starts immediately. Default: false

Architecture

Claude Code (runs normally)
         |
~/.claude/projects/*/sessions/*.jsonl
         |
LogMonitor (background daemon)
    |-- Detects rate limit patterns
    |-- Sends OS notification
    |-- Sets flag file for shell
         |
Shell Functions
    |-- claude-api: switch to API mode
    |-- claude-sub: switch to subscription

Files

File	Purpose
~/.claude_fallback.pid	Monitor PID (daemon mode)
~/.claude_fallback_state.json	Current mode and status
~/.claude_fallback_active	Flag file when limit detected
~/.claude_fallback_error.log	Error log

Requirements

• Python 3.8+
• Active Claude Pro or Max subscription
• Anthropic API key (for fallback)
• Claude Code installed
• macOS or Linux (Windows via WSL)

Real-World Usage

My typical workflow:

1. Start a coding session with claude
2. Background monitor watches the session logs
3. Work normally until I hit subscription limits
4. Get a native OS notification
5. Exit Claude Code and run claude-api to switch
6. Continue working in the same directory
7. When done with heavy work, run claude-sub to switch back

Subscription + API fallback typically costs $5-10/month in API usage, far less than going API-only. Usage varies based on codebase size and model choice (Opus uses ~5x more than Sonnet).

Security Notes

• Store your API key in environment variables
• The tool only reads/writes the ANTHROPIC_API_KEY environment variable
• All logs are stored locally
• Your API key is never transmitted except to Anthropic's API

Contributing

Contributions welcome! This project addresses a real need expressed in Anthropic's GitHub Issue #2944.

1. Fork the repository
2. Create a feature branch
3. Commit your changes
4. Push to the branch
5. Open a Pull Request

Disclaimer

This is an unofficial tool not affiliated with Anthropic. Use at your own risk. Always monitor your API usage and costs. The tool respects Anthropic's terms of service by only switching between legitimate authentication methods.

License

Apache 2.0 License - see LICENSE file for details

Acknowledgments

• Inspired by Issue #2944
• Built for developers who need uninterrupted coding sessions
• Thanks to the Anthropic team for building Claude Code