Anthropic replaced Git in its monorepo with Scion, and the lazy reading is "Git doesn't scale." The real break was checkout volume. Almost every client was a CI job or an agent sandbox: always online, short-lived, created by the million. For those, a full local clone is pure overhead, and several hundred mirrors stopped helping.
Scion moves the work to the server. Clients ask for the exact objects they lack, and every query is also an API. Anthropic reports 99%+ cache hits, a 200x smaller footprint than the mirror fleet, and 25% of CI CPU freed.
You can't install it, but two ideas work on plain Git today. Stop cloning to ask questions: a small service that owns one mirror can answer "what changed?" and "what's the merge base?" for every job. And make checkout cost follow the change:
git clone --filter=blob:none --no-checkout --sparse "$REPO_URL" src
git -C src sparse-checkout set --cone services/payments build
git -C src checkout --detach "$HEAD_SHA"
The query service in about 100 lines of Python, where sparse checkouts break, and how Scion compares to Sapling, Piper and Scalar: Anthropic Scion vs Git: what agent-scale source control changes
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