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.
Illustration · not a photoHow this story was checked
- ResearchedWith AI assistance · 3 sources
- AI source checkEach sentence matched to its source
- Editor approvalMayank Sahu · 15 Oct, 12:20
- Published15 Oct, 12:20
Verify this story
- 3 sources, 1 official · 3 with an archived copy · see sources
- Every fact has a label and a source number · fact ledger
- What we searched, read and could not verify · research note
- Machine-readable: facts as JSON · text as Markdown
How this was made: researched, drafted and source-checked by AI (Claude, made by Anthropic), then published under the editor’s standing approval. A person did not read it line by line before it went live. AI policy
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.13
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.12 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
How labels workQuestions readers ask
Can I download Scion?
No. Anthropic’s post says Scion is internal and shares only design ideas.
Why did Anthropic stop using Git?
Anthropic says merges grew past 30,000 a day and Git mirroring became hard to run at that scale.
What is the Mononoke criticism?
A developer who worked on Meta’s Mononoke says Scion’s design closely follows it and asks Anthropic to credit it.