Anthropic says AI-written code has outgrown tools built for human scale, so it built Scion and moved its monorepo off git in five months.
Anthropic reports that coding is no longer its main bottleneck, because Claude can iterate on research loops and build services at high speed. The strain has shifted to developer infrastructure such as source control, builds, and CI. The company says it merged around 2,500 code changes per day in May 2026 and over 30,000 per day by September.
Git's design, where every clone is a complete offline repository, no longer fits the monorepo. Anthropic says the main branch history alone is almost 100 GB, and it performs about 25 million checkouts per day for CI. At its peak the company ran several hundred internal git mirrors, which became harder to operate as the merge rate rose.
Scion starts from the observation that nearly all clients are agents and jobs that are always online. The server handles history, blame, commits, merges, and rebases, while the client keeps a bounded local cache and can work with sparse or virtualized checkouts. Every source control query is also available through an API, so many jobs need no local repository at all. Data is content-addressed, which lets servers scale horizontally and cache freely.
The basic unit is a server-side changeset in a write-ahead log, with extra structures for blame and path history computed as derived data. Anthropic notes that it also shipped a code review surface called Antique and code search in the same period, and expects other AI-heavy teams to hit similar limits.
Source: Hacker News (front page)
