Anthropic replaces git with in-house Scion
Anthropic has moved its monorepo off git onto Scion, a version control system it built in-house, after Claude-driven code merges grew twelvefold in four months and overwhelmed infrastructure designed for human developers.
Anthropic described how agent-written code pushed its developer infrastructure past what git could handle. The company averaged about 2,500 merged code changes per day in May 2026. By September, it was merging more than 30,000 per day.
"Coding is no longer the bottleneck," the post says. The pressure now falls on source control, builds and CI. Anthropic built Scion and fully migrated its monorepo in five months. In the same period it also shipped a code review tool called Antique, code search and a source-control IAM system.
The numbers explain why. History on the main branch is nearly 100 GB, and a compressed working copy is over 25 GB. The company runs about 25 million checkouts per day for CI alone, which would mean more than 600 PB of git traffic per day if fetched naively. At peak, Anthropic operated several hundred internal git mirrors and used shallow clones, sparse checkouts and blob-storage snapshots. Those workarounds got harder to maintain as the merge rate climbed.
Scion assumes nearly every client is an always-online agent or job. The server handles history, blame, commits, merges and rebases. Clients keep only a bounded local cache. Every client query is also exposed through an API, so many jobs need no local repository at all. Anthropic says this makes its automated bisect and revert pipelines practical at scale. The system is horizontally scalable, and no full copy of the repo exists anywhere. The design draws on Google's Piper and Meta's Sapling.
Anthropic says it expects other heavy users of AI coding tools to run into the same limits before long.