Anthropic replaces Git with Scion after merges jump from 2,500 to 30,000 a day
Anthropic says a seven-person team built Scion, an in-house server-centric version control system, and migrated its monorepo off Git in five months as Claude-driven coding made source control the bottleneck.
Photo: The wub / Wikimedia Commons, CC BY-SA 4.0. Anthropic logo via Wikimedia Commons (public domain).
Anthropic published an engineering post on October 13 explaining how it fully migrated its monorepo from Git to Scion, an in-house version control system, in five months. The company said daily merges rose from about 2,500 in May 2026 to more than 30,000 by September as Claude wrote software at a scale that broke human-era developer infrastructure.
Scion is designed as a server-centric system for always-online agents and jobs, rather than Git's offline, complete-clone model. Anthropic said the history of its main branch alone is nearly 100 GB, a compressed working copy exceeds 25 GB, and CI alone performs on the order of 25 million code checkouts a day. At peak it operated several hundred internal Git mirrors before switching approaches.
In Scion, commits, merges, rebases, history and blame run on the server; clients keep a bounded object cache and use sparse or virtualized checkouts. Anthropic says its Scion infrastructure footprint is now about 200 times smaller in CPU and memory than the prior Git mirroring setup, and that CI and research jobs check out code in seconds rather than minutes, yielding a roughly 25% CPU capacity win for CI alone. These are Anthropic's own figures.
A team of seven also shipped Antique, a code review surface, plus code search and IAM in the same period. Anthropic says Scion is not a general Git replacement for most organizations, but that its ideas—richer server-side APIs and better sparse/shallow composition—could help Git platforms scale for agentic coding. It credited Claude Mythos Preview and Claude Tag with both creating the merge surge and accelerating Scion's construction.