Anthropic ditched git for self-built Scion as Claude pushed merges to 30k/day
AGI Hunt · wechat · 2026-10-14
Anthropic's engineering blog details its 5-month, 7-person migration of its monorepo from git to self-built VCS Scion. Daily merges jumped from 2,500 in May to 30,000+ in September (30,401 on Sep 9), driven by Claude.
Why git broke: main branch history near 100GB; CI does 25M checkouts/day (600PB+ if full clones). They ran hundreds of git mirrors but realized clients are mostly always-online agents — git's distributed offline design was the bottleneck.
Scion design: server-side blame/diff/merge via API; cheap lockless commits with cost proportional to change size, not repo size; changesets store only deltas, with recursively-defined derived data for blame/history; a 3-tier cache with 99%+ hit rates.
Results: infra CPU/memory at 1/200 of the mirror setup; CI reclaimed 25% CPU; agent worktree creation fell from 7.1 min to 5.1 sec; per-change VCS time from 34 to 3.7 minutes (11k agent-hours saved daily).
How they worked: had Claude rewrite the git import pipeline (1/20 memory, 4x speed); engineers now see Claude as a stronger coder, with their value in design tradeoffs and saying no to over-engineering.
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