# Anthropic replaces Git with custom Scion source control system

> **Key takeaway:** Anthropic built a custom source control system called Scion to handle massive scale, managing over 30,000 daily merges and 25 million daily checkouts.

**Published:** 2026-10-13T23:00:06+00:00 
**Source:** Simon Willison Web & Open Source 
**Category:** software-engineering 
**Canonical URL:** https://fosswire.org/news/anthropic-replaces-git-with-custom-scion-source-control-syst.html 

## Summary
Due to a massive increase in code change velocity, Anthropic has migrated from Git to a custom-built source control system named Scion. The move was driven by extreme scale requirements, including a 100 GB main branch history and the need to avoid massive Git traffic overhead. The new system includes a code review component called Antique and was developed by a seven-person team over five months.

## Technical scale of Scion
- **Scale requirements**: The main branch history is nearly 100 GB, with a compressed working copy exceeding 25 GB.
- **Throughput**: The system handles approximately 25 million code checkouts per day for CI, developer environments, and agent sandboxes.
- **Architecture**: Scion utilizes a "derived data" concept inspired by Meta's Sapling (Mononoke) and Google's Piper.
- **Connectivity**: The system lacks offline support because its primary user, the Claude AI, is always online.
- **Review system**: A new code review system named Antique is used alongside Scion.

## Why it matters
This demonstrates how extreme AI-driven development velocity can outpace the performance capabilities of standard distributed version control systems like Git.