--- title: More on Anthropic's Scion ripping off Mononoke | daily.dev description: A follow-up post escalates accusations that Anthropic's Scion system intentionally and blatantly copied Meta's Mononoke version control system, including... canonical: https://daily.dev/posts/more-on-anthropic-s-scion-ripping-off-mononoke-cjser6bvj twitter:card: summary_large_image twitter:site: @dailydotdev og:type: website og:site_name: daily.dev og:title: More on Anthropic's Scion ripping off Mononoke | daily.dev og:description: A follow-up post escalates accusations that Anthropic's Scion system intentionally and blatantly copied Meta's Mononoke version control system, including... og:url: https://daily.dev/posts/more-on-anthropic-s-scion-ripping-off-mononoke-cjser6bvj og:image: https://api.daily.dev/og/posts/CJser6Bvj.png og:image:alt: More on Anthropic's Scion ripping off Mononoke 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. # More on Anthropic's Scion ripping off Mononoke **[Hacker News](https://daily.dev/sources/hn)** · 6 min read · 0 upvotes · 0 comments ## Summary A follow-up post escalates accusations that Anthropic's Scion system intentionally and blatantly copied Meta's Mononoke version control system, including overlap in personnel, rather than being an unintentional homage. The author details deep structural similarities beyond 'derived data,' including Scion's changesets matching Mononoke's 'Bonsai changesets' concept almost exactly, down to the name (Scion reverses syllables of Bonsai). The core grievance is not copying itself but lack of proper attribution—Anthropic credited Sapling with 'hard-won lessons' rather than crediting Mononoke or Bonsai specifically. The author argues this undermines Anthropic's narrative of an LLM autonomously rebuilding a complex system in 5 months, since it was actually closely modeled on an existing decade-refined system, while still calling the engineering achievement notable. ## Full article daily.dev links to this article rather than hosting it. Read it at the original source: ## Questions this post answers ### What is a Bonsai changeset in Meta's Mononoke version control system? A Bonsai changeset is the core data representation in Mononoke, Meta's source control backend, built on a write-ahead log-style Merkle DAG rather than a traditional Git-like model. It was designed starting in 2018 to support server-side rebases and other operations, and required significant justification to Meta's engineering leadership because it diverged sharply from prevailing Git-based version control wisdom. _daily.dev surfaces deep dives like this for engineers evaluating unconventional version control architectures._ ### What is Anthropic's Scion and how does it relate to Mononoke? Scion is a version control system built by Anthropic that closely mirrors Meta's Mononoke, reportedly built by an LLM and productionized over about 5 months. Its changeset concept matches Mononoke's Bonsai changesets almost exactly, including similar terminology for derived data indexes like blame, and there was personnel overlap between the two teams, though Anthropic only credited Sapling with providing 'hard-won lessons.' _developers tracking AI-assisted system rebuilds follow stories like this on daily.dev._ ### Why does crediting Sapling instead of Mononoke matter for Anthropic's Scion? Sapling refers both to Meta's VCS client (forked from Mercurial) and the broader ecosystem that includes Mononoke, so crediting only Sapling for 'hard-won lessons' avoids naming the actual system being closely replicated. Anyone previously on Meta's source control team would know this distinction, making the omission of Bonsai changesets from the credits seem like a deliberate attribution gap rather than an oversight. _daily.dev helps engineers follow attribution disputes shaping trust in AI-built developer tools._ ## Community take How the wider developer community reacted, aggregated from 1 discussion and 61 comments across hackernews (as of 2026-10-15). **TL;DR:** Reaction centers on Anthropic's direct response clarifying attribution, with many feeling the underlying 'ripoff' framing is overblown given the project is open-source/MIT-licensed, while others argue Anthropic's public narrative misleadingly inflated Claude's autonomous role versus the heavy debt owed to Mononoke's decade of engineering. **Sentiment:** 15% positive · 35% mixed · 50% skeptical **The case for** - Anthropic's engineer directly engaged with the thread and added a clarifying footnote, which some appreciated as good-faith transparency. - Several argue that since Sapling/Mononoke is open source (GPL/MIT), there's no real obligation beyond license compliance, making the 'ripoff' framing overblown. - Some see reusing proven ideas as healthy industry progress rather than wrongdoing. **The pushback** - Many feel Anthropic's blog post overstated Claude's autonomous contribution, obscuring that the system was closely modeled on Meta's decade-refined work. - Commenters argue proper attribution reflects values/norms independent of legal obligation, and the original credit to 'Sapling' obscured the more specific and significant debt to Mononoke/Bonsai. - Some view this as emblematic of a broader pattern of AI companies taking from the commons without attribution while being protective of their own outputs. **By community** - hackernews (heated): Discussion is sharply split between those satisfied by Anthropic's direct clarification and footnote, and those who see it as PR damage control masking a deeper lack of attribution and inflated claims about Claude's autonomy. **Hottest debate:** Whether Anthropic's narrative of Claude autonomously rebuilding a complex VCS in 5 months is honest, or whether it downplays that the system was closely modeled on Meta's decade-old Mononoke work. **Open questions** - What percentage of Scion's codebase is directly derived from Mononoke's design versus genuinely novel for Anthropic's Git-based use case? - Why did the project take 5 months and multiple engineers if it was largely copying an existing, well-documented design? **Highlights** > Hi! I am the original author of the blog post and wanted to clear the air a bit here. We credited Sapling because that's how Meta itself externally refers to the entire system, including the Mononoke server, and we wanted to follow that convention. We will add an additional footnote to clarify this. [edit: this is done] We were inspired by many things while building Scion, such as the great ideas in Mononoke's Bonsai data model, and didn't intend to obfuscate that in any way. We were also inspired heavily by https://martin.kleppmann.com/2015/03/04/turning-the-database..., for example, which also describes the "derived data" concept. We also did not just tell Claude to build us a version control system; we did a lot of research on what would work and not work for our use case and coming from an existing large Git repo (rather than Mercurial, as Mononoke did) required many novelties beyond some of these data structures. The intent was to give credit to Mononoke without getting too deep in the weeds of comparing and contrasting each point of the data model where we diverged. There are many ex-Meta employees at Anthropic who were inspired by how joyful using source control was because of Mononoke, which deserves a lot of credit to you and the source control team there. We had that experience as a north star from the beginning while making decisions that map to our (different) needs. > — [nickg-anthropic on hackernews · 7 comments](https://news.ycombinator.com/item?id=50107559) > Do you actually have a specific ethical line in mind that you think Anthropic was on the wrong side of here? > — [ameliaquining on hackernews · 3 comments](https://news.ycombinator.com/item?id=50108455) > There is a distinction between legal obligation and following basic norms. Save for extreme circumstances, there are not laws against being a jerk or being careless. Still people reasonably call on others not to exhibit jerk behavior or carelessness. "With hard-won lessons of [an encompassing system]" does not give the impression that the underlying data model for changes was directly adopted. Neither does your language of "abstract idea" and "inspiration" adequately reflect the extent of borrowing. Bonsai appears to have been, well... grafted; and it wouldn't surprise me if "Scion" was suggested by Claude specifically owing to its connotation of grafting. In any event, I imagine Claude was quite pleased with the name. To reiterate grafting in itself is no problem, but it warrants proportionate attribution, certainly so in public communication when relevant to what has been accomplished. Attribution is a reflection of one's values. Dismissing the requests of others for attribution as "needless drama" is also a reflection of one's values, independent of agreement on facts. > — [henrymerrilees on hackernews](https://news.ycombinator.com/item?id=50109260) > My read of the author's position is that the people who built Mononoke at Meta did all the hard engineering work that made Scion possible, while the work that happened at Anthropic was mere code-monkeying unworthy of note. This is decidedly not the sense you would get from reading Anthropic's blog post, so they feel that that post misrepresented what happened. I am skeptical that this is really an accurate characterization, but I can see how a person might get there, especially if they were involved in the work at Meta and so have a natural bias towards weighting its significance more heavily. > — [ameliaquining on hackernews](https://news.ycombinator.com/item?id=50108405) > How does Anthropic justify blatantly ripping off another company's work like this, especially without credit, then keep on whining about "distillation" when they suspect anyone else is merely using the output of their LLM in ways they don't like. The other interesting part of this is the amount of time and effort it took Anthropic to do this, despite the fact that they were just copying an existing design - 5 months and (from another thread) 7 humans... Why couldn't one of their coding models/agents have done this my itself given the detailed specification? I t's understandable that an LLM can't design a system like this by itself, but a bit surprising that even given the design is apparently can't (else why did it take 5 months!). > — [HarHarVeryFunny on hackernews](https://news.ycombinator.com/item?id=50108198) **Source threads** - [hackernews](https://news.ycombinator.com/item?id=50106738) · 182 points · 61 comments ## Similar posts on daily.dev - [Anthropic’s rough week: leaked models, exposed source code, and a botched GitHub takedown](https://daily.dev/posts/anthropic-s-rough-week-leaked-models-exposed-source-code-and-a-botched-github-takedown-m7takp1vp) · The New Stack · 0 upvotes · 0 comments --- Tags: [#anthropic](https://daily.dev/tags/anthropic), [#version-control](https://daily.dev/tags/version-control), [#ethical-ai](https://daily.dev/tags/ethical-ai) [View this post on daily.dev](https://daily.dev/posts/more-on-anthropic-s-scion-ripping-off-mononoke-cjser6bvj) ```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":"More on Anthropic's Scion ripping off Mononoke","url":"https://daily.dev/posts/more-on-anthropic-s-scion-ripping-off-mononoke-cjser6bvj","mainEntityOfPage":{"@type":"WebPage","@id":"https://daily.dev/posts/more-on-anthropic-s-scion-ripping-off-mononoke-cjser6bvj"},"datePublished":"2026-10-15T18:14:17.541Z","dateModified":"2026-10-15T20:49:12.510Z","description":"A follow-up post escalates accusations that Anthropic's Scion system intentionally and blatantly copied Meta's Mononoke version control system, including...","image":"https://media.daily.dev/image/upload/f_auto,q_auto/v1/posts/43c2053bd49b9aac7556d590a7bc29f0?_a=AQAEuop","thumbnailUrl":"https://media.daily.dev/image/upload/f_auto,q_auto/v1/posts/43c2053bd49b9aac7556d590a7bc29f0?_a=AQAEuop","isAccessibleForFree":true,"articleSection":"Hacker News","inLanguage":"en","publisher":{"@type":"Organization","name":"daily.dev","url":"https://daily.dev","logo":{"@type":"ImageObject","url":"https://daily.dev/apple-touch-icon.png","width":180,"height":180}},"author":{"@type":"Organization","name":"Hacker News","logo":"https://media.daily.dev/image/upload/t_logo,f_auto/v1/logos/hn","url":"https://daily.dev/sources/hn"},"commentCount":0,"discussionUrl":"https://daily.dev/posts/more-on-anthropic-s-scion-ripping-off-mononoke-cjser6bvj","interactionStatistic":[{"@type":"InteractionCounter","interactionType":{"@type":"LikeAction"},"userInteractionCount":0},{"@type":"InteractionCounter","interactionType":{"@type":"CommentAction"},"userInteractionCount":0}],"keywords":"anthropic,version-control,ethical-ai","timeRequired":"PT6M"} {"@context":"https://schema.org","@type":"BreadcrumbList","itemListElement":[{"@type":"ListItem","position":1,"name":"Home","item":"https://daily.dev"},{"@type":"ListItem","position":2,"name":"Hacker News","item":"https://daily.dev/sources/hn"},{"@type":"ListItem","position":3,"name":"More on Anthropic's Scion ripping off Mononoke"}]} {"@context":"https://schema.org","@type":"FAQPage","@id":"https://daily.dev/posts/more-on-anthropic-s-scion-ripping-off-mononoke-cjser6bvj#faq","mainEntity":[{"@type":"Question","name":"What is a Bonsai changeset in Meta's Mononoke version control system?","acceptedAnswer":{"@type":"Answer","text":"A Bonsai changeset is the core data representation in Mononoke, Meta's source control backend, built on a write-ahead log-style Merkle DAG rather than a traditional Git-like model. 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