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

What happened

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

Reported by 2 sources

The story so far

Anthropic built Scion, its own version control system, and fully migrated its monorepo from Git in five months to address infrastructure bottlenecks as daily merged code changes rose from around 2,500 in May to more than 30,000 in September. Anthropic said seven people built the system, with its repository approaching 100 GB of main-branch history and CI performing roughly 25 million checkouts a day. Scion retrieves files on demand, moves operations to the server, and uses layered caches with reported hit rates above 99%. Anthropic reported that median agent workspace startup time fell from 7.1 minutes to 5.1 seconds. In his explanation of Anthropic’s engineering write-up, Baoyu emphasized that Scion is intended for exceptionally large monorepos and that the company does not plan to make it a general-purpose Git replacement.

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