Anthropic replaces Git with an in-house VCS built for agent-scale merges
Scion replaces Git across Anthropic's monorepo after daily merges grew from 2,500 to over 30,000 in four months, driven largely by Claude committing code itself.
Anthropic published an engineering post on 13 October explaining why it stopped using Git for its main monorepo and built a replacement called Scion. The team says source control had become its biggest development bottleneck: daily merges grew from around 2,500 in May 2026 to more than 30,000 by September, a jump Anthropic attributes largely to Claude itself writing, reviewing and landing code rather than to more human engineers joining.
A team of seven built Scion, a code review tool called Antique, code search and a new source control IAM system, and migrated the whole monorepo in five months. Anthropic reports CI checkout times improved by two orders of magnitude and its Git-mirroring infrastructure footprint shrank 200-fold, alongside a 25% CPU capacity win in CI.
Why it matters: this is a concrete data point on what happens to a Git-centric workflow once an AI agent starts generating most of the commits rather than reviewing or assisting with them. Most teams are nowhere near 30,000 merges a day, but the direction of travel, agents committing at a pace humans never did, is worth factoring into any assumption that your current source control setup scales indefinitely with heavier agentic use.
The caveat: Scion is internal tooling. Anthropic hasn’t open-sourced it or said it plans to, so there’s nothing here to install, only a warning about where the bottleneck moves to next.