Anthropic’s daily code merges grew over tenfold in months. Source control became the main bottleneck. The company built Scion, an in-house version control system. It migrated its monorepo from Git in five months. Scion assumes clients are always online. It uses a server-centric design with bounded local caches. Commits are server-side, cheap, and lock-free. Working copies are optional and sparse by design. Scion cut CPU and memory use by 200x versus Git mirrors. CI jobs now check out code in seconds, not minutes. CI alone saved 25% CPU capacity. Claude Mythos Preview rewrote a key pipeline to be 20x more memory-efficient and 4x faster.
What changed
Anthropic used Git with hundreds of internal mirrors and repository snapshots to handle scale.
What it unlocks
Handling tens of millions of daily checkouts without per-client repository copies.
- 2,500 to 30,000 merges per day
- 100 GB main branch history
- 25 GB compressed working copy
- 25M code checkouts per day for CI
Sources