Anthropic Migrates Its Monorepo From Git to Scion as Code Changes Surge

1. 08:28
   宝玉 · XPicks

   Why Anthropic built Scion to replace git for its monorepo

   Drawing on Anthropic’s engineering blog, Baoyu explains why the company replaced git with Scion as daily merged code changes grew from around 2,500 in May to more than 30,000 in September. Scion retrieves files on demand, moves operations to the server, and uses layered caches with hit rates above 99%. Anthropic reports that median agent workspace startup fell from 7.1 minutes to 5.1 seconds, while emphasizing that Scion serves exceptionally large monorepos and is not a general-purpose git replacement.

2. 07:00
   Simon WillisonPicks

   How Anthropic redesigned source control with Scion

   Simon Willison highlights Anthropic’s explanation of Scion, its custom alternative to Git, as merged code changes grew from around 2,500 per day in May 2026 to over 30,000 per day in September. Anthropic reports almost 100 GB of main-branch history and roughly 25 million daily CI checkouts; seven people built the system, completing migration in five months. Willison speculates that Fable/Mythos class models contributed to the increased coding velocity and connects Anthropic’s experience with adversarial review to his own, including the need for engineers to steer models away from over-engineering.

3. 00:36
   Anthropic · XPicks

   Anthropic explains building in-house source control and migrating its monorepo from git

   Anthropic’s Engineering blog shares how it built a new version control system and fully migrated its monorepo from git in five months. In May, it merged around 2,500 code changes per day; in September, it merged more than 30,000 per day. That growth created bottlenecks in developer infrastructure built for human rather than agent scale: https://www.anthropic.com/engineering/redesigning-source-control

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