Anthropic builds Scion, a custom source control system, to keep up with AI-written code

Anthropic has replaced Git with a homegrown source control system called Scion. The reason is simple: its engineers, and increasingly its AI models, are now merging more than 30,000 code changes every day. From 2,500 merges to 30,000 In May 2026, Anthropic averaged roughly 2,500 merged code changes per day. By September 2026, that figure had climbed past 30,000 merges per day. The company attributes the surge to the growing capabilities of its Claude models. Claude increasingly handles coding tasks on its own, which means code is being produced at a rate that looks less like a team of engineers and more like a factory floor. Anthropic’s main branch history was approaching 100 GB, and the system was handling tens of millions of checkouts each day. Seven engineers, five months Rather than patch the old setup, Anthropic built a new one. A team of just seven engineers designed Scion and completed the full migration of the company’s monorepo in five months. Scion borrows design ideas from two systems built by companies that faced similar scale problems: Google’s Piper and Meta’s Sapling. Scion uses always-online clients, meaning the developer’s tools stay connected to central servers ra...