---
title: "Anthropic says it replaced Git with its own source control system, Scion, after daily merges passed 30,000"
url: https://anawords.com/story/anthropic-scion-source-control-replaces-git-monorepo
published: 2026-10-15T12:20:51+05:30
updated: 2026-10-15T12:20:51+05:30
section: Tools & Apps
author: Mayank Sahu
checked: sources checked by AI, approved by editor
version: 1
---

# Anthropic says it replaced Git with its own source control system, Scion, after daily merges passed 30,000

Scion is internal and not open source. A developer who helped build Meta’s Mononoke says Anthropic’s design write-up closely follows Mononoke’s and should credit it.

**In short:** Anthropic said on 13 October 2026 that it moved its monorepo from Git to Scion, a version control system it built in-house, after daily merges rose from about 2,500 in May to over 30,000 in September. Scion is not open source. A former Mononoke developer says the design should credit Meta’s work.

## What Anthropic described

In an engineering post published on 13 October 2026, Anthropic said it had “fully migrated our monorepo from git in five months” to Scion, a source control system it built itself.[^1] Anthropic says merges into the monorepo grew from about 2,500 a day in May 2026 to over 30,000 a day by September.[^1]

Anthropic gives these figures for the scale involved:[^1]

- The main branch history is almost 100 GB; a compressed working copy is over 25 GB.
- About 25 million CI checkouts happen a day.
- At peak it ran several hundred internal Git mirrors.

It argues Git’s offline, distributed design fits poorly with always-online clients such as AI agents and CI jobs.[^1]

## Anthropic’s claims

Anthropic says Scion’s infrastructure is “200x smaller” in CPU and memory than its old Git mirroring setup, and that checkouts take seconds instead of minutes.[^1] It says a seven-person team built Scion and a code review tool, Antique, in five months.[^1] These are Anthropic’s own measurements.

## What is released

Nothing. Scion is internal; the post shares design ideas and suggests Git platforms could adopt some of them.[^1] Some summaries described Scion as open source; Anthropic’s post does not say that.[^1][^3]

## The credit question

On 14 October, a developer who writes as “sunshowers” and says they helped build Mononoke, Meta’s open-source source control server, argued that Scion’s “derived data” design closely tracks Mononoke’s.[^2] Anthropic’s post credits Google’s Piper and Meta’s Sapling but does not mention Mononoke.[^1][^2] The developer says they do not object to the ideas being reused, but asks Anthropic to give credit.[^2] We did not find a response from Anthropic.

*Disclosure: Anawords uses Claude, made by Anthropic, as one of its research tools. Anthropic has no say in our coverage.*

## Fact ledger

- [Confirmed] Anthropic moved its monorepo from Git to its in-house system, Scion, in five months. (source 1)
- [Company claim] Daily merges grew from about 2,500 in May 2026 to over 30,000 in September. (source 1)
- [Company claim] Scion’s infrastructure is 200x smaller than the old Git mirrors. (source 1)
- [Confirmed] Scion is internal and has not been released as open source. (source 1)
- [Confirmed] A former Mononoke developer says Scion’s design closely follows Mononoke and should credit it. (source 2)
- [Not known] Whether Anthropic will respond to the credit criticism.

## Sources

1. [Anthropic Engineering: Redesigning source control](https://www.anthropic.com/engineering/redesigning-source-control) — official
2. [sunshowers: Anthropic’s Scion and Mononoke](https://sunshowers.io/posts/anthropic-mononoke/)
3. [AI Weekly: Anthropic builds Scion to replace Git](https://aiweekly.co/alerts/anthropic-builds-scion-to-replace-git-after-merges-hit-30000day)