Anthropic Scion: Why They Replaced Git at 30,000 Merges/Day Anthropic built a custom source control system called Scion after its daily merged code changes rose from about 2,500 in May 2026 to over 30,000 by September 2026, straining Git and its roughly 25 million daily CI checkouts. Seven engineers spent five months on Scion, which moves commits, rebases and merges server-side, exposes source control queries as APIs and cut the infrastructure footprint to 200 times smaller than Anthropic's previous Git mirror fleet. Anthropic says Scion is closed source and "is by no means a suitable replacement for git for general use," while GitLab is separately building a Git-compatible next-generation SCM that it says completes some workloads up to 50 times faster. Anthropic hit 30,000 merged code changes in a single day and Git buckled under the pressure. So they spent five months and seven engineers building a custom source control system from scratch. The result, Scion, is not coming to a package manager near you — but the problem it solves is heading your way regardless. Git Was Fine — Until It Wasn’t In May 2026, Anthropic averaged around 2,500 code changes merged per day. By September, that number was over 30,000. Claude was writing code faster than their infrastructure could process it. The monorepo’s main branch ballooned to nearly 100 GB of history. CI systems were performing approximately 25 million code checkouts per day, before counting developer environments, agent sandboxes, and research jobs. Naive git fetching at that rate would have generated over 600 petabytes of network traffic daily. The team tried every trick in the standard Git scaling playbook: shallow clones, sparse checkouts, promisor remotes, repository snapshots, and several hundred Git mirrors running in parallel. Eventually, the workarounds became harder to maintain than the original problem. So they built something new. What Scion Actually Does Scion inverts Git’s core assumption. Where Git distributes full repository copies to clients — enabling offline work — Scion puts everything on the server. Commits, rebases, and merges all happen server-side. Clients maintain bounded caches and files materialize on demand. Source control queries are exposed as APIs, so CI jobs often skip having a local repository entirely. InfoQ’s breakdown of the architecture https://www.infoq.com/news/2026/10/anthropic-source-control/ covers the internal mechanics in useful detail. The unit of work is a “changeset”: an entry in a write-ahead log that stores file deltas and content-addressed blob pointers. Regional caches feed from authoritative servers backed by Spanner and cloud storage, achieving over 99% hit rates at every tier. Infrastructure footprint came in at 200 times smaller than their previous Git mirror fleet. CI checkouts dropped from minutes to seconds. The Part You Should Actually Care About Scion is closed source. Anthropic is explicit that it “is by no means a suitable replacement for git for general use” and only makes sense for enormous monorepos with tens of thousands of engineers or swarms of agents. You are not getting this. But that is the wrong lesson. The more important signal is the trajectory: 2,500 to 30,000 merges per day in four months. Anthropic notes that “the latent demand for merging code is practically infinite” and expects similar challenges industry-wide within six to twelve months. Their engineers reported a telling shift in workflow: “Very often, we found that the role of the engineers was to tell Claude ‘no’.” Coding is no longer the bottleneck. Developer infrastructure designed for human-scale output is. What You Can Do Today You do not need to build Scion. Git’s sparse checkout https://git-scm.com/docs/git-sparse-checkout handles early-stage scaling pressure if you use it deliberately: Sparse checkout for CI — fetch only what your job needs git clone --filter=blob:none --sparse