Anthropic details Scion, a git replacement for its monorepo, built by seven engineers with Claude in five months, as daily merges rose from 2,500 in May to 30K+

As our merges per day grew more than tenfold, source control became our biggest development bottleneck.

Anthropic 2026-10-14

Context & Ripple Effects

Anthropic had already expanded Claude Code with dynamic workflows that run hundreds of subagents in parallel and said that Claude authored more than 80% of code merged into its codebase. The resulting increase in software output shifted the limiting problem from generating code to integrating it safely through a shared repository.

Scion is Anthropic's response to that operational constraint: a seven-engineer team used Claude to build an in-house replacement for Git in five months. Public reaction focused on the corresponding human role in reviewing and rejecting agent output, rather than merely producing it.

First-order effects

Anthropic replaces Git for its monorepo with Scion as daily merge volume rises from roughly 2,500 in May to more than 30,000, targeting source control as its immediate engineering bottleneck.
The project demonstrates that a small Anthropic team can use Claude to build infrastructure for managing the code output that Claude helps generate.

Second-order effects

Anthropic's engineering workflow must place greater weight on integration, validation, and human review as agent-generated changes arrive faster than conventional source-control processes can absorb them.
The earlier claim that Claude authored most merged code becomes operationally consequential: repository infrastructure, not just coding assistants, must scale with agent-driven development.

Third-order effects

If this pattern holds, source control evolves into an agentic development control plane that coordinates high-volume machine-authored changes rather than chiefly serving individual developers.
Closed, in-house tooling may become a differentiator for AI labs whose internal code volume and workflows exceed what general-purpose developer tools are designed to handle.

The trend: AI-assisted software development is moving the bottleneck from code creation toward the control planes that validate, merge, and govern agent-generated changes.

Discussion

@dbreunig Drew Breunig on x
“Very often, we found that the role of the engineers was to tell Claude ‘no.’” This is now the job! Push the model out of distribution when describing what you want and when reviewing its work! Our work is communicating and enforcing our intent.
@beyarkay Boyd Kane on x
I really want to know what happened during “quiet week”
@anthropicai @anthropicai on x
New on our Engineering blog: Creating in-house source control. In May, we merged around 2,500 code changes per day. In September, we merged more than 30,000 per day. As a result, we became bottlenecked by developer infrastructure built for human (rather than agent) scale. Here, w…
@paularambles @paularambles on x
the future of software engineering is gentle parenting for agents
@scaling01 @scaling01 on x
Half of Anthropic's 2026 code merges happened in just 50 days
@gergelyorosz Gergely Orosz on x
While an interesting read and ambitious project, like anything else Anthropic creates (model, harness, tools) this tool is once more closed source, seemingly no plans to open it up for the outside world to observe or learn from it. Only thing open at Ant is Bun and MCP 😞 [embedde…
@andrewcurran_ Andrew Curran on x
Anthropic's code changes merged per day has 10x since May. 'Claude is able to autonomously iterate on research loops, micro-optimize complex programs, and build new services from the ground up at a speed and scale we haven't seen before.'
@tokengremlin @tokengremlin on x
In short: Fable 5.5 is the best model in the world, and we're releasing it in the next few days.
@kimmonismus @kimmonismus on x
Talking about recursive self improvement: “Claude is able to autonomously iterate on research loops, micro-optimize complex programs, and build new services from the ground up at a speed and scale we haven't seen before.” Even if we haven't quite reached RSI yet, it's incredibly …
@sweis Steve Weis on x
One year ago, I would have thought replacing an entrenched source-control vendor with homegrown source control and code review systems was a terrible idea. I saw these projects take years before. It was done in 5 months and is supporting 10X the volume. https://www.anthropic.com/…
@kentcdodds Kent C. Dodds on x
Anthropic built its own git and github replacement called scion and antique. Built for agents. https://www.anthropic.com/...
@yuchenj_uw Yuchen Jin on x
“In May 2026, Anthropic averaged around 2,500 code changes merged per day; as of September, we merged over 30,000 per day.” 12x growth in just 4 months. This explains why GitHub keeps breaking.
@atmoio @atmoio on x
In a few years no 100+ person company will use Git anymore. Its design is seriously archaic. Just look at what's happened to GitHub.
@scaling01 @scaling01 on x
Some findings based on Anthropic's published plot: - The share of merges on weekends rose steadily from 7% to 18% (+0.33 pts/week). Monday-Wednesday declined the most, Thursday slightly, and Friday held steady. - The time to double the number of daily merges shortened from 67 day…
@bentlegen Ben Vinegar on x
Anthropic merging 10x more code since May feels bonkers I can feel us going way faster (~2.5x since May), but that's not even close
@dexhorthy Dex on x
anthropic built their own git. Most interesting mental shift here, and if you buy that changing code happens more and more autonomously, faster*, then this will make a ton of sense: Git was designed so that any client could serve the repo. Fully offline, your *build time* dev sta…
@davidcrespo @davidcrespo on bluesky
excellent post for people interested in dev infrastructure
@andrewnez@mastodon.social Andrew Nesbitt on mastodon
This sounds an awful lot like SVN to me 🤔 — https://www.anthropic.com/...
r/ClaudeAI r on reddit
Redesigning source control at Anthropic
r/theprimeagen r on reddit
Redesigning source control at Anthropic
r/artificial r on reddit
Anthropic says coding is no longer the bottleneck. Its monorepo hit 30,000+ merges in a day.
@me2resh @me2resh on x
I predicted this to happen. Lately GitHub lost its value. It became a delivery medium for ai agents to keep track of its changes. It was about time to have agents forge their own medium.
@leilavclark Leila Clark on x
I find most Anthropic blog posts pretty overrated, but this one is actually really cool! I've also been quite frustrated with how slow and clunky Git feels for an agent-first era. This is a ncie solution. Also unlike a lot of Anthropic blog posts, I think this one is pretty clear…
@_rrdelaney Ryan Delaney on x
It's finally time to ditch git for source control! Big tech has largely already figured this out, but git really doesn't scale, for all the reasons mentioned in the article. Google, Meta, etc. have all moved on, because it turns out swarms of engineers working at FAANG look a lot…
@pdrmnvd Pedram.Md on x
The team that worked on this is incredible. It was a completely painless migration for me, and what they built was so much faster and easier to use. More great work by great people, very happy that we share it.
@johnalanwoods John Woods on x
Anthropic vibe-coded its way out of Git and into a proprietary, always-online, centralized mess, then called losing 20 years of distributed-systems learnings an architectural breakthrough. Intelligence != Wisdom.
@bstaples Bill Staples on x
We announced next-gen SCM at Transcend in June, with Nick from Anthropic on stage. Their new post shows why: merges went from 2,500 to 30,000+ a day in four months. They built Scion for their unique needs, enterprises will need that scale on Git, governed end to end, cloud or air…
@jimstewartson @jimstewartson on x
Mark my words. Anthropic's codebase is going to start cracking. They have no fucking idea what it does anymore. 30,000 code changes per day is absurd by 3 or 4 orders of magnitude. They're just churning tokens, hoping it magically becomes intelligent by itself. It's pathetic.
@steveklabnik Steve Klabnik on x
very excited to see this out of A\ this is our thesis at @erscio ! But we are building a git compatibility layer: https://ersc.io/... enterprise adoption of new source control is a big ask, so making a smooth bridge from the past to the future is a big part of our offer
@badvertexdev @badvertexdev on x
our butt was making so much poop we had to invent a new kind of toilet
@pcalcado @pcalcado on x
Any startup that hires enough ex-Googlers ends up with an ad hoc, informally-specified, bug-ridden, slow implementation of half of Google infra
@cgtwts @cgtwts on x
RIP Git
@adocomplete Ado on x
Big problems need even bigger solutions.
@danielmiessler @danielmiessler on x
Anthropic has replaced Git internally. The titans are falling.
@rynorhn Ryan Orhan on x
holy shit, we're actually reaching the point where the tools we've used to write software for decades are starting to become obsolete for ai-heavy development. anthropic has already moved its entire monorepo off git. i genuinely wonder what github looks like in 3 years.
@rjs Ryan Singer on x
Interesting
@macaesbruno Bruno Maçães on x
This post is quite scary. But not the superintelligence kind of scary. More the financial implosion kind. Anthropic no longer seems to operate as a business
@vaibhavsisinty Vaibhav Sisinty on x
Anthropic moved its entire codebase off Git And this is much bigger than it looks Claude writes so much of Anthropic's code now that merged changes went from 2,500 a day in May to over 30,000 a day by September Git was built for humans, working offline, with a full copy of the co…
@ziv_ravid Ravid Shwartz Ziv on x
How Anthropic's new engineering post would read without the PR: Seven engineers, assisted by Claude, built and migrated to a new source control system in five months, handling 30,000 merges a day and reducing infrastructure CPU and memory requirements by 200x. The system builds o…
@wholemars @wholemars on x
This is pretty insane. Anthropic was committing so much Claudeslop (2,500 changes a day) that it literally broke their Git Monorepo. They had Claude write a new version control system called Scion where all the commits happen on the server, since the AI agents don't work offline …
@scottstts Scott on x
Anthropic merges code 30000 times per day now, forget about RSI for a moment and just think about that. anthropic is probably one of the few companies that use AI internally to the extreme. You can kinda use that as a measure of how your org is doing in comparison
@__nmca__ Nat McAleese on x
“claude, migrate us off git. make no mistakes”
@amorriscode Anthony Morris on x
wish i worked on this tbh. it's cool how fast our tech is changing.
@evisdrenova Evis Drenova on x
this is a fun read. my biggest takeaway -> local is p much dead. no one is really designing for “local only” like they used to. if you pull on that thread, what other design constraints go out of the window... https://www.anthropic.com/...
r/technology r on reddit
Anthropic moving to in-house version control system in five months
r/programming r on reddit
Anthropic designs new in-house monorepo source control system “Scion”, code review tool “Antique”, designed for massive scale

Chronicles