--- title: Redesigning source control at Anthropic | daily.dev description: Anthropic replaced git with an in-house version control system called Scion to handle growth in code merges. Merges jumped from about 2,500 per day in May 2026... canonical: https://daily.dev/posts/redesigning-source-control-at-anthropic-h0zfzbh1m twitter:card: summary_large_image twitter:site: @dailydotdev og:type: website og:site_name: daily.dev og:title: Redesigning source control at Anthropic | daily.dev og:description: Anthropic replaced git with an in-house version control system called Scion to handle growth in code merges. Merges jumped from about 2,500 per day in May 2026... og:url: https://daily.dev/posts/redesigning-source-control-at-anthropic-h0zfzbh1m og:image: https://api.daily.dev/og/posts/H0ZfZBh1M.png og:image:alt: Redesigning source control at Anthropic og:image:width: 1200 og:image:height: 630 og:locale: en --- > ## Documentation Index > Fetch the complete documentation index at: https://daily.dev/llms.txt > Use this file to discover all available pages before exploring further. # Redesigning source control at Anthropic **[Reid Burke](https://daily.dev/sources/reidburke)** · 19 min read · 0 upvotes · 1 comments ## Summary Anthropic replaced git with an in-house version control system called Scion to handle growth in code merges. Merges jumped from about 2,500 per day in May 2026 to over 30,000 per day by September. Git's main branch history hit nearly 100 GB, with a compressed working copy over 25 GB, and CI and other jobs performed around 25 million checkouts daily. Scion assumes clients are always online, keeps the server authoritative, and skips packfiles and repo maintenance entirely. A seven-person team built Scion plus a code review tool called Antique and migrated the whole monorepo in five months. The new infrastructure uses 200x less CPU and memory than the old git mirror fleet, and checkouts run two orders of magnitude faster. ## Full article daily.dev links to this article rather than hosting it. Read it at the original source: ## Questions this post answers ### Why did Anthropic stop using git for their monorepo and build their own version control system? Anthropic's merge rate grew from about 2,500 code changes per day in May 2026 to over 30,000 per day by September, mostly driven by AI agents writing code. Git's design assumes offline-capable clients needing full repo copies, but nearly all of Anthropic's clients were always-online agents and CI jobs performing around 25 million checkouts daily, so they built an in-house system called Scion instead. _Developers hitting monorepo scaling limits can follow source control architecture shifts like this on daily.dev._ ### How does Anthropic's Scion version control system differ architecturally from git? Scion assumes clients are always online, so the server (not the client) handles commits, merges, rebases, and history queries, while the client keeps only a bounded local cache. There are no packfiles or required repository maintenance, data is content-addressed and horizontally scalable, and checkouts are sparse or virtualized so clients only fetch the files they actually need. _Teams weighing custom infra against git's defaults can track these design tradeoffs on daily.dev._ ### How long did it take Anthropic to build and migrate to their custom source control system? A team of seven engineers built Scion along with a code review tool called Antique and several related systems, fully migrating Anthropic's monorepo from git in five months, while merge volume increased tenfold during that same period. The team also reported Scion's infrastructure footprint is 200 times smaller in CPU and memory than their previous git mirroring setup. _Engineers scoping fast infra migrations can see real-world timelines like this on daily.dev._ ## Community discussion Top comments from developers on daily.dev. **@nark3d** · 0 upvotes > You've dropped the merge queue for post-merge and pre-deploy testing, which works while Claude can out-fix the conflicts. Semantic conflicts need a look: two changes merge cleanly, the tests pass on both, and only the combination is wrong. I'd make the post-merge run build the combined tree and run the e2e suite against it. Does post-merge testing catch that? ## Similar posts on daily.dev - [An online-first version control system in this agentic era](https://daily.dev/posts/an-online-first-version-control-system-in-this-agentic-era-j2oxfrzb2) · Amit Merchant · 27 upvotes · 2 comments --- Tags: [#ai-agents](https://daily.dev/tags/ai-agents), [#career](https://daily.dev/tags/career), [#git](https://daily.dev/tags/git), [#anthropic](https://daily.dev/tags/anthropic), [#version-control](https://daily.dev/tags/version-control) [View this post on daily.dev](https://daily.dev/posts/redesigning-source-control-at-anthropic-h0zfzbh1m) ```json {"@context":"https://schema.org","@graph":[{"@type":"Organization","@id":"https://daily.dev/#organization","name":"daily.dev","url":"https://daily.dev","logo":{"@type":"ImageObject","url":"https://daily.dev/apple-touch-icon.png","width":180,"height":180},"sameAs":["https://twitter.com/dailydotdev","https://github.com/dailydotdev","https://www.linkedin.com/company/daily-dev-ltd"]},{"@type":"WebSite","@id":"https://daily.dev/#website","url":"https://daily.dev","name":"daily.dev","publisher":{"@id":"https://daily.dev/#organization"},"potentialAction":{"@type":"SearchAction","target":{"@type":"EntryPoint","urlTemplate":"https://daily.dev/search?q={search_term_string}"},"query-input":"required name=search_term_string"}}]} {"@context":"https://schema.org","@type":"TechArticle","headline":"Redesigning source control at Anthropic","url":"https://daily.dev/posts/redesigning-source-control-at-anthropic-h0zfzbh1m","mainEntityOfPage":{"@type":"WebPage","@id":"https://daily.dev/posts/redesigning-source-control-at-anthropic-h0zfzbh1m"},"datePublished":"2026-10-27T05:59:33.158Z","dateModified":"2026-10-27T06:00:06.376Z","description":"Anthropic replaced git with an in-house version control system called Scion to handle growth in code merges. 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Semantic conflicts need a look: two changes merge cleanly, the tests pass on both, and only the combination is wrong. I’d make the post-merge run build the combined tree and run the e2e suite against it. Does post-merge testing catch that?","datePublished":"2026-10-28T17:25:07.147Z","url":"https://daily.dev/posts/H0ZfZBh1M#c-GQCouG3b5","author":{"@type":"Person","name":"Adam","url":"https://daily.dev/nark3d","image":"https://avatars.githubusercontent.com/u/2162621?v=4"}}]} {"@context":"https://schema.org","@type":"FAQPage","@id":"https://daily.dev/posts/redesigning-source-control-at-anthropic-h0zfzbh1m#faq","mainEntity":[{"@type":"Question","name":"Why did Anthropic stop using git for their monorepo and build their own version control system?","acceptedAnswer":{"@type":"Answer","text":"Anthropic's merge rate grew from about 2,500 code changes per day in May 2026 to over 30,000 per day by September, mostly driven by AI agents writing code. 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