Anthropic replaces git with in-house Scion as monorepo merges reach 30,000 a day

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Anthropic replaces git with in-house Scion as monorepo merges reach 30,000 a day

Anthropic's monorepo merges rose from about 2,500 code changes per day in May 2026 to over 30,000 per day by September, making source control its biggest development bottleneck.
The team built Scion, an in-house version control system, and fully migrated the monorepo away from git in five months.
The main branch history is almost 100 GB and a compressed working copy is over 25 GB, with about 25 million CI checkouts per day.
At peak Anthropic ran several hundred internal git mirrors, but seeds drifted from the tip of main between refreshes and became harder to run as merges grew.
Scion puts the server at the center, handling history, blame, commits, merges, and rebases, while clients keep only a bounded local cache because agents are always online.

Hacker News opinions

Commit the prompts and let the generated code sit in the repo as build output? That's basically Spec Driven Development already. The catch is the prompt is a conversation, so a SPEC.md always loses nuance.

Reproducible LLM output would need a seeded PRNG, which sounds fine in theory. In practice I doubt hosted models give you that.

Looks like version control for big game and 3D assets. Neat.

The 600 PB number is 25 million checkouts times the 25 GB compressed copy, so fetched naively just means a full clone on every checkout. Nobody should do that.

That 100 GB history is the odd part. I've seen agents do weird things with git, which makes me think people are using git history as a message queue.

They say they don't let agents coordinate through source control like that. The growth in code is what made Scion necessary.

Claude Mythos Preview rewrote their git-to-Scion ingestion pipeline and cut memory use 20x while running 4x faster. It's a one-time import, though, so does it matter that much?

East River Source Control is building a git compatibility layer for this same problem. Google and Meta hit this wall over a decade ago.

I wonder if Pijul could work as a non-git backend, since its patch model looks like Scion's and it already has a forge.

So Anthropic reinvented Perforce more than SVN.