Anthropic Replaced Git: 2,500 Daily Commits Became 30,000, So They Rewrote Source Control
Anthropic rebuilt source control from scratch after its daily merge rate rose more than 12x in four months, and the resulting system, Scion, abandons Git's distributed model entirely.
Anthropic has disclosed that it designed and deployed a custom source control system, Scion, to replace Git after its code-change velocity exploded. In May 2026 the company averaged around 2,500 code changes merged per day; by September that figure exceeded 30,000 per day. The main branch history alone is almost 100 GB, a compressed working copy is over 25 GB, and CI performs on the order of 25 million checkouts per day — which, fetched naively, would mean over 600 PB of Git traffic daily. The new system was built by a team of seven people, and the migration from Git was completed in five months.
Scion is described as a reinvention of centralized source control along the lines of Subversion, rather than another distributed system. Anthropic also built a new code review system called Antique alongside it. When asked on Hacker News about the lack of offline support, Scion engineer Nick G said that since Claude is by far the heaviest user of Scion and is necessarily online, offline support simply wasn't important to build.
Anthropic also makes extensive use of adversarial review in its development process. The article notes that while this is incredibly effective in many ways, it can also be myopic: skilled engineers needed to steer Claude away from over-engineering parts of the system in response to hypothetical concerns. Willison speculates that the introduction of Fable/Mythos class models is a key factor in the increased coding velocity, and his annotated chart of the commit-rate increase marks public release dates of Anthropic's 2026 models.