Anthropic built Scion, an in-house VCS, after merges hit 30,000 a day

Anthropic published on 13 October 2026 how it redesigned source control for agent-scale coding. Merges to its monorepo rose from about 2,500 a day in May 2026 to over 30,000 a day by September. Main-branch history alone is almost 100 GB, a compressed working copy over 25 GB, and CI alone does on the order of 25 million checkouts a day. Git mirrors and seeds stopped scaling, so a seven-person team built Scion, an always-online, client-server VCS inspired by Google Piper and Meta Sapling, and migrated the monorepo from git in five months. They also shipped Antique (code review), code search, and IAM in the same window. Scion stores changesets of files changed vs the first parent, builds derived data such as blame and path history, and keeps checkouts sparse or virtualised. Anthropic says Scion's infrastructure footprint is about 200x smaller in CPU and memory than prior git mirroring, CI checkouts are seconds instead of minutes, and CI alone gained about 25% CPU capacity. Scion is not open sourced; Anthropic says it only fits enormous monorepos with agent swarms. Claims are Anthropic's own. On Hacker News (499 points, ~496 comments), one camp says agent-scale repos need Piper-like designs. Another says reinventing VCS is wasteful and Perforce or better git servers might have been enough. A third debates whether 30,000 merges a day is sustainable or meaningful history. No consensus. Sorted take: most teams will not need Scion. The useful signal is that agent volume breaks human-scale git ops, so watch merge queues, sparse checkouts, and review capacity before you hit the same wall.