alt Hacker NewsRedesigning source control at Anthropic
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> As our monorepo grows, it increasingly doesn’t fit that design space. The history of our main branch alone is almost 100 GB
The first thing that hits me is, did you consider not going all in on a monorepo? I know it has been the trend in general, but it seems a bit of a red flag when you go from "let's have a monorepo it will make merging easier" to "let's redesign version control because merging is too hard" without the middle question "should we really have a monorepo?"
As a derivative thought I'm curious if AI tooling is tipping people more towards monorepos now since it gives the agent the whole context of the app in one go? Or is this independent - I can easily check out 5 repos in one directory and run an agent there.
What is are the benefits of supporting extremely high churn rate in version control? What is the code doing? What problems are being solved? Are changing requirements the driving factor, and if so, why are requirement changes accelerating?
> ..., the latent demand for merging code is practically infinite, and every bottleneck we remove immediately leads to a further increase in the amount of code we produce.
If the goal is to write software which solves real problems, how can the demand for code grow infinitely?
It's not open sourced in case you are wondering.
My first real job was at Oracle. At the time Oracle started to write their own source control system (and move off of clearcase, which was a very reasonable thing to do).
The guy who ran that project called it his "$LASTNAME law" that every large company will at some point write their own source control system.
I laughed.
About a year later I went to Google, and within a couple of years Google also did the same thing.
Not at all surprised. Git was just good enough (and cheap enough) the companies didn't need to do this to escape the {phsyical scaling, cost scaling} problems that most commercial SCM systems had.
I don't get one thing, if agents are so great at developing software at massive scale, why wouldn't Anthropic, instead of just selling tokens to other companies to use its agents, let those agents develop highly profitable services for Anthropic to support their IPO valuation or not require raising money at all? For example, a competitor to Google search.
The Scion project seems like a great example of identifying and addressing scaling issues (just in time, it seems). Just 7 engineers! It makes me think I'd pay Anthropic $300K/year to work on such problems.
But it's a sad example, for open-source and for small engineering companies. Instead of infrastructure being more easily shared with the collective, or valued enough to build a business, now companies can tailor even major infrastructure to their own needs, and avoid all that coordination.
I'm glad they publish their notes to encourage others, but I suspect we're entering an epoch where confidentiality matters most.
Anthropic's problem was merging code at scale, but the scale problem I have with SCM is really merging all the related docs; these get lost in a stream of a forest of comments, PR's, and documentation, all of which (like a wiki) goes rapidly out of date before anyone notices because none of it is automatically correlated.
So it's a SVN/Perforce style server based VCS with a more modern design. Sounds exactly like Lore from Epic Games but with zero production use outside the company and no support for non text assets. And they won't release the code.
> Earlier in the year, we had largely handwritten the first version of the git-to-Scion ingestion pipeline as a prototype. We thought it was good—until we got our hands on an early internal snapshot of Claude Mythos Preview. We asked it to rewrite the whole thing, and with no further instructions, it produced a version that consumed 20x less memory and was 4x faster, while preserving all of the implicit invariants around ingestion ordering and data structures.
I feel like the advantage of having these models in house can't be understated. Companies with access to inferior models, trying to compete, will be left in the dust when it comes to general development.
This article doesn't do a very good job of convincing me that git is technically incapable of handling the described workload. There are a lot of steps between vanilla git and building your own VCS from zero.
If I was an investor I would be on the phone with Dario asking why we are wasting engineering talent on reinventing source control and churning the product with 30k pulls per day.
Not to downplay Anthropic's engineering work here, but I suspect we'll see a lot more reinvention of the wheel, even at smaller startups, as AI makes writing code significantly cheaper.
The tradeoff between building something custom and adapting an existing solution is changing. Whether maintaining all that custom software turns out to be equally cheap is another question.
Every now and then I like to browse the claude code release notes just to get a sense of the number of changes in that product over time. There's little choice but to simply count bullet points if you want to try to quantify it, but it's interesting how that count over time compares with the charts in this article:
Honest question: at this point, what do people do at Anthropic?
It sounds like Claude loops on itself and must be pushing millions of lines of code changes per day. Even the humans can’t type commit fast enough. Are these people soon to be laid off?
> As our monorepo grows, it increasingly doesn’t fit that design space. The history of our main branch alone is almost 100 GB, and a compressed working copy is over 25 GB. We perform on the order of 25 million code checkouts per day for CI, before counting developer environments, agent sandboxes, and research jobs. Fetched naively, that would be over 600 PB of git traffic per day.
I read this and wonder what their agents have committed into the repo that people aren't looking at for _that much size_? Do they have a ton of binary assets in there or something??
great article. Besides the source control stuff, I found this very interesting (and matches my experience with agentic coding in general, now we'll see until hiring pipelines will take this kind of skillset into account). I am not sure however how easy it is to review 30k PRs/day even if only for intent, and how one can easily notice if the model is taking shortcuts on implementing said intent without reading the code...
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Engineers are no less valuable, but their work is changing. All of the engineers who worked on this system would now rate Claude as better at writing code than them. But our engineers still supplied the invaluable understanding of the high-level inter-system components and the design-level tradeoffs, making informed choices around the problems we wanted to solve and the scale we knew we needed to achieve. Very often, we found that the role of the engineers was to tell Claude “no.” Agents will sometimes violate core system constraints to satisfy a pattern that should never have been allowed in the first place. This was particularly common in our migration. For example, there were multiple systems that tried to brute force looking up when a change merged to main by linearly reading the commit log instead of asking our code review tool. Anthropic also makes extensive use of adversarial review, and, while this is incredibly effective in many ways, it can also be myopic, so skilled engineers needed to steer Claude away from over-engineering parts of the system in response to hypothetical concerns. For example, one such review was overly defensive about trusting another internal service, which resulted in Claude adding excessive validation and complexity. Our team members still review every change request for the system, but they now examine the intent of the change as opposed to reading every line of code.
> as of September, we merged over 30,000 per day.
There's going to be an ugly phase where everybody FOMOs into thinking they need to do the same, only to realize that they're not Anthropic/Google/etc.
How much is the sheer volume of slop code that AI generates reduced by if you simply specify that you want it to be both minimalist and readable, getting it to think hard about architecture and completely rearchitecting requirements change? Surely if AI is so smart and useful it should be able to manage that?
> 30k merges per day
> 25 million CI checkouts
833 checkouts for every merge? That's quite a few. Even accounting for multiple environments at different stages of production readiness, that's pretty weird.
This is maybe a little less revolutionary than people are treating it? A lot of large tech companies (Google, Facebook, Microsoft) have already built their own homegrown SCM (or have implemented custom extensions to Git), because Git and other SCMs don't handle their scale. Most interesting thing about Scion is how quickly it was deployed.
I don't think this SCM stores only code. I think more than 80% of it consists of tests and various types of gold data. All of this is constantly changing, and we need to keep track of it somehow.
Why can't I rack my brain around why this is needed? I have had zero issues using git with agentic coding.
> Anthropic uses Claude to write software far more than almost any other company
Who's beating Anthropic here lol
I guess Anthropic are not IEC-62443-4-1 compliant, because I doubt a human reads and understands every single line of those 30,000 merges a day.
What then?
This is a nice thoughtful article.
If Anthropic has the best coding model, harness and the best software development methodologies and systems. And then, they scale all that up, with no constrains on their tokens. On top of that, they have access to all kind of ideas their models getting trained on when millions are chatting with it - then in theory they can build any software better than anyone out there. And same goes to science and math..
> In Scion, every commit, rebase, or merge happens on the server, so there’s nothing to push...
I think this is the wrong way to solve problems and goes the wrong way toward solving real problems.
> as of September, we merged over 30,000 per day.
Their Website/CLI seems keeping the same? What did they do?
Is this really something to be proud of? I make heavy use of AI, but for anything that is eventually going to production there's still a human reviewer. Based on this I assume Anthropic is shipping code with no human review? Is the future of our industry going to be oneshotting prompts with out manual code review and then having AI fix the bugs found in production buy customers? I'm not trying to be a Curmudgeon, but am I missing something?
> In May 2026, Anthropic averaged around 2,500 code changes merged per day; as of September, we merged over 30,000 per day.
Here are the public model releases from Anthropic this year:
5th Feb 2026: Claude Opus 4.6
17th Feb 2026: Claude Sonnet 4.6
7th Apr 2026: Claude Mythos Preview
16th Apr 2026: Claude Opus 4.7
28th May 2026: Claude Opus 4.8
9th Jun 2026: Claude Fable 5
9th Jun 2026: Claude Mythos 5
30th Jun 2026: Claude Sonnet 5
24th Jul 2026: Claude Opus 5
1st Sep 2026: Claude Fable 5.1
1st Sep 2026: Claude Mythos 5.1
22nd Sep 2026: Claude Opus 5.5
28th Sep 2026: Claude Sonnet 5.5
7th Oct 2026: Claude Haiku 5.5
I would guess that any public model has been available internally for at least a month before that date, maybe longer.
My best guess is that the uptick in code changes corresponds to the availability of Mythos/Fable-class models inside of Anthropic.
This sounds more like a trash pile than a source control system. Anthropic is spewing out code for codes sake. They cant possibly manage it, the more they generate the more they will realize they are just regurgitating training data for no real purpose that can serve anyone.
And for this they buy disk? Maybe this is irresponsible use of technology.
It would be nice if you could just commit the prompts as your "source code", and let the AI-generated code sit in the repo as a kind of expensive-to-generate build output.
One of the reasons to move to systems like this (not always spoken to explicitly) is to reduce the risk of accidental or deliberate exfiltration of code (esp when paired with build servers and remote deploy etc.). Basically nobody’s laptop ever holds much of a buildable codebase.
Google migrated from Perforce to Piper, and Meta migrated from Mercurial to Sapling.
Now Anthropic has migrated from Git to Scion. It's a good sign they are on the right track.
This is the wrong way to look at the problem. Maybe they should have asked, "Why does our process need to do so many git checkouts?" Why can't you just run the tests where you already checked out the code?
This is... surprisingly small?
From what I recall, Google's repo is closer to 80 terabytes.
Slightly OT, but it‘s interesting and nice to see that Anthropic‘s own blog posts don‘t have many AI prose tells (or Claude-isms) in them.
This is interesting to me, as I was thinking of adding a Git server to my AI orchestrator when I eventually need to split agent containers off of the main machine (to make agent CPU horizontally scalable).
Maybe I should just bite the bullet and use a different VCS system entirely once I get there, which has most of the Anthropic system's properties (including being much faster) but doesn't need to be horizontally scalable.
>Changes merged to our monorepo
> monorepo
Well, there's your problem.
I'm curious what this "Antropic Antique" is. As I understand code review the tightest bottleneck for a lot of Claude Code users, and I'm curious how this would help with that.
Making scalable source control is much easier when you can rely on a distributed database (Spanner) and object storage (GCS/S3/...)!
Where does all of this end? If they keep this growth up, or even if they slow to a linear growth, they will produce more code than humanity combined pre-AI. That's scary.
How does this compare to Google's in-house source control?
Most companies don't use mono-repos like this. While there are some really compelling advantages, the downsides tend to stack up as a company's codevbase grows.
It's mainly just startups and huge companies. For small companies git works fine for mono-repos and large companies can build their own complex code management pipelines for mono-repos.
I have been questioning whether agentic development changes the mono-repo vs multi-repo question.
> as of September, we merged over 30,000 per day.
I just wonder what is the churn rate (and the cost per LOC) here.
Can you estimate the total number of tokens you used to create this new system?
What seems inevitable is that the frontier labs will be able to recreate every piece of software better than the current offerings, and after that everyone will just be a vendor of the frontier labs
> Fetched naively, that would be over 600 PB of git traffic per day.
This seems like an absurd amount of data / traffic per day. Is there really that much to code that needs changing on a daily basis?
For a broader look on scaling other parts of software development outside of source control, Adam Bender's talk from earlier this year ("Software engineering at the tipping point") has some good ideas: https://youtu.be/2n41YjR5QfU
Excuse me for throwing up this stupid idea, but if code changes per unit of time keep growing at this rate and are not slowing down with infinite merging demand, it seems that this repo will be in a constant state of continuous change and we constantly roll forward with automated code and obviously no direct human supervision, then why even have source control? Why not just let software be fluid and, like Heraclitus river, never step twice in the same repo.