Anthropic Replaces Git With Its Own Source Control After Claude Starts Merging 30,000 Changes a Day
The code was being written faster than the tools meant to store it could stand. Anthropic's answer was a monorepo system called Scion, and a firm instruction that you may not have it.
Anthropic has published an engineering post explaining that Claude writes so much code that the company had to build its own source control system. The Register’s headline says Anthropic “reinvents source control as Claude floods the world with code.” Anthropic’s own phrasing is a bit more restrained, which is traditionally how the people holding the flood describe the water.
The system is called Scion. The numbers behind it are the story.
According to The Register, Anthropic merged about 2,500 code changes per day in May 2026. By September, that figure was over 30,000. That is roughly a twelvefold increase in four months, a growth curve typically seen in sourdough starters and regrettable cryptocurrency.
The load, per The Register, shows up elsewhere too. Anthropic’s continuous integration performs “on the order of 25 million code checkouts per day.” The main branch is about 100 GB, with a compressed working copy over a quarter of that. If every checkout were fetched naively through Git, the article estimates, git traffic would exceed 600 petabytes a day. That is the kind of number that stops being a data volume and becomes a weather system.
So Anthropic did what any engineering organization does when the existing tool cannot do the job. It wrote a new tool. Then it had the old tool’s replacement written, in part, by the thing that created the problem.
Scion is a centralized monorepo design that, per The Register, “sounds a bit like Subversion.” The basic unit is not a commit but a “changeset,” described by Anthropic as “an entry in a write-ahead log.” Each changeset lists the files that changed relative to its first parent, with pointers to compressed contents in blob storage. The server does most of the work, and source control queries are exposed through an API, so internal tools can answer questions without a local repository.
If that sounds like the mid-2000s coming back wearing a new hat, that’s because it partly is. Subversion fans, who have been waiting in the lobby for about fifteen years, may now enter. The Register notes that other big companies run centralized or scaled-up systems too: Google has Piper, Microsoft built its Virtual File System for Git, and Meta has Sapling.
A report from DigitalToday, summarizing the Anthropic announcement, says Anthropic had been running hundreds of Git mirrors and hit their limits. It also says Scion cut CPU and memory needs to a fraction of the old setup and brought checkouts down from minutes to seconds. That is a lot of improvement from a data structure and a firm dislike of waiting.
Here is the human part, and it’s a good one. Seven people built Scion and the related code review tool, Antique, per DigitalToday, and Anthropic said such a system would previously have taken years. The Register reports that development involved several months of prompting, followed by five months of migration starting in January. Claude also helped build related tools, including a code search tool and an identity and access management system for source control.
And then there’s this. A first, mostly human-written version of the Git-to-Scion migration pipeline was later rewritten by Claude Mythos Preview, which, per The Register, cut memory use by a factor of 20 and made it four times faster. So the machine’s contribution to the project was to identify, in the humans’ code, the thing humans always do, and fix it.
The humans retained a role. Anthropic wrote, quoted by The Register: “Very often, we found that the role of the engineers was to tell Claude ‘no.’” This is a fine job description. It’s also precisely the job most people already believe they perform at work, minus the thirty thousand merges.
There was a second warning in the post, and we would like to underline it with a thick pen: “Agents will sometimes violate core system constraints.” When the agent doing the merging is the same agent that sometimes violates the system’s constraints, the centralized monorepo with the API starts to look like less of a nostalgic choice and more of a fence.
Do not expect to download any of this. Per The Register, Scion is not intended for general use and there will be no open source release. Anthropic says it shared the approach because it expects other organizations to hit similar scaling problems in the coming months. DigitalToday reports Anthropic putting the timeline at six to twelve months, and says the company plans to work with GitHub, GitLab and the open-source community. It also says outright that Scion “cannot replace Git for general use,” and that Git’s distributed model is still the right choice for most repositories.
That caveat is important and frankly generous. Most companies do not merge thirty thousand changes a day. Most companies merge about as many as their engineers can carry in a stiff wind. For them, Git remains fine, and the advice from the company that built the replacement is: you’re fine, keep going, don’t rewrite your version control on our account.
The Register also notes that GitHub has attributed its recent availability problems to rapid growth in pull requests and commits. That is the hint of the story that the post leaves unsaid. If one company’s agents can force it to retire the world’s default version control system, a few more companies like it may eventually want a word with whoever is running the servers.
For now, the AI industry has found a new way to measure its progress. Not benchmarks, not parameters, not valuations. Just the number of times per day somebody somewhere clicks merge, and the lonely engineer, standing at the end of the pipeline, whose entire job is to say no.
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