Discussion

• @karpathy Andrej Karpathy on x

  This is a super exciting release - Claude Fable 5 is the same underlying model as Mythos but with added safeguards.  The benchmarks are great and it's SOTA on everything by a margin but I'll add that *qualitatively* also, this is a major-version-bump-deserving step change forward…

• @danshipper Dan Shipper on x

  BREAKING: Anthropic just dropped Claude Fable 5—this is Mythos, made safe for public release. It is the best coding model in the world. We've been testing it internally @every for the last week or so across coding, writing, marketing, editing, and more—here's our vibe check: - [v…

• @claudeai Claude on x

  Introducing Claude Fable 5: a Mythos-class model that we've made safe for general use. Its capabilities exceed those of any model we've ever made generally available. [video]

• @felixrieseberg Felix Rieseberg on x

  Today, we're introducing Claude Fable 5 and Mythos 5, two configurations of our next major language model. I'd normally highlight the numbers: It's SOTA on nearly all benchmarks. I want to talk about something else, because with Fable 5 out in the world, I think a third era

• @claudeai Claude on x

  Fable 5's safeguards detect requests related to cybersecurity, biology and chemistry, and distillation. Users are informed whenever a fallback occurs—on average in less than 5% of sessions. We'll keep refining the safeguards to reduce false positives.

• @claudeai Claude on x

  Fable 5 is state-of-the-art on nearly all tested benchmarks, with exceptional performance in software engineering, knowledge work, scientific research, and vision. The longer and more complex the task, the larger Fable 5's lead over our other models. [image]

• @altryne Alex Volkov on x

  This is fascinating.  This is what made Anthropic decide that it's near CB2 - Without AI tools the task they were given was estimated in 40-95 days, with Mythos 5, two person team accomplished this task in 16 hours.  While being generalists!

• @cheatyyyy @cheatyyyy on x

  Claude Fable 5 specifically has a serverside flag that will allow people to try it out with their plan until a certain date, after which it will be gated behind usage credits. it is over bros, we're not getting to use this model for long with subsidized pricing [image]

• @zephyr_z9 @zephyr_z9 on x

  Well they don't have the infra to serve 200B+ active param model U will have to wait till Rubin or pray that they distill it well in Opus 5

• @mikeyk Mike Krieger on x

  Claude Fable 5 is out today. The first Mythos-class model everyone can use & the first model I hand off whole projects to. This weekend I built a self-maintaining, proactive media tracker for myself, over 2 days with Fable taking large chunks at a time [image]

• @altryne Alex Volkov on x

  Very interesting new restriction, you cannot use Fable 5 to accelerate ML and LLM development!? Things like training pipelines, pretraining, distributed infrastructure and ML Accelerator design! Anthropic is keeping it's edge with these models and sandbagging everyone else! [imag…

• @fabknowledge @fabknowledge on x

  Total victory.... holy shit [image]

• @eliebakouch Elie on x

  wow claude mythos/fable benchmark scores are insane [image]

• @scaling01 @scaling01 on x

  Looks like a scaled up version of GPT-5.5 could beat Mythos 5 [image]

• @bcherny Boris Cherny on x

  Fable 5 is the biggest step up I've felt in our models since Opus 4.5 back in November.  After 4.5 came out I uninstalled my IDE when I realized that I'd been doing 100% of my coding in a terminal for a few weeks.  With Fable, it's felt like Claude has stepped up from being a cod…

• @levie Aaron Levie on x

  If you thought AI progress was slowing down, well here's the immediate answer to that. Huge jump in capability across the board. This is going to deliver major improvement in agents across almost all knowledge work categories. [image]

• @cursor_ai @cursor_ai on x

  Claude Fable 5 is now available in Cursor. It sets a new state of the art on CursorBench at 72.9%, 8 points above the previous best. [image]

• @zapier @zapier on x

  Claude Fable 5 is the new top score on AutomationBench: 17.4% Best where precision is the whole job: Ops, HR, anything long-running where the model needs to recover, not quit [image]

• @altryne Alex Volkov on x

  NEW: Anthropic releases 2 “mythos” models which advance their capability frontier! Fable 5: will have additional safeguards in topics related to Cyber and Biology Mythos 5: Will continue to be available via Project Glasswing System Card is out, so let's read together. [image]

• @alexalbert__ Alex Albert on x

  I've been at Anthropic through every model launch. There's been a few cases I can remember of a launch that stands out and marks a step-change in how we use models: - Claude Opus 3 - Claude Sonnet 3.5 - Claude Opus 4.5 And now Claude Fable 5. With Fable, the model stopped

• @sashadem Sasha de Marigny on x

  The tenor and complexity of model launches have changed completely over the past few months. Fable 5 felt like a transition into an entirely new chapter of AI's story. And the quest to enable the strengths of these models while preventing their risks has never felt more urgent.

• @swyx @swyx on x

  Mythos is live! so excited to have our FrontierCode recognized as the next frontier coding bench. on FC Diamond, BOTH Opus 4.8 and GPT 5.5 don't meaningfully scale with effort, which many of you caught yesterday. Mythos/Fable posttraining have really applied that test time [image…

• @yuchenj_uw Yuchen Jin on x

  Claude Fable 5 / Mythos 5 wins everywhere.  I thought Fable 5 was just a nerfed Mythos Preview, but it's literally better.  SWE-Bench Pro: Fable 5: 80.3%, GPT-5.5: 58.6%.  And the price is only 2x Opus 4.8: $10/input MTok, $50/output MTok.  I don't think GPT 5.6 can beat this...

• @illscience Anish Acharya on x

  A few notes on Fable 5: - It's interesting that it routes certain requests to 4.8 behind the scenes - in this case it's for safety but if you squint you can imagine a cost optimization where queries are classified and routed based on the amount of intelligence needed - Calling [i…

• @natolambert Nathan Lambert on x

  If anthropic can't convince a bunch of tech bro's on X that they're not safety washing, good luck convincing the american public.

• @claudeai Claude on x

  Releasing a model this capable comes with risks. Without safeguards, Fable 5's capabilities in areas like cybersecurity could be misused to cause serious damage. Queries on a narrow range of topics will instead receive a response from our next-most-capable model, Opus 4.8. [video…

• @arrakis_ai Choi on x

  Claude Fable 5 Benchmark [image]

• @peterwildeford Peter Wildeford on x

  Props to the @AnthropicAI marketing team. They successfully scared us with the name “Mythos” and now that they want us to use it, its morphed into the cute and cuddly “Fable” [image]

• @scaling01 @scaling01 on x

  “Mythos 5 is likely unable to fully and reliably automate R&D for frontier projects spanning multiple weeks” [image]

• @bindureddy Bindu Reddy on x

  Results from Internal Coding Evals For Claude Fable - For 98% of tasks, it simply does the same thing as GPT 5.5 or Opus 4.8 and costs 2x - For 2% of hard coding tasks, it does make sense if you are willing to pay double and get some quality gains So ideally, you want to

• @mweinbach Max Weinbach on x

  Claude Fable 5 (Mythos 5 with safeguards in place, same weights) It's available today, but only available as part of the Claude sub until June 22nd then it will cost extra at API rates. After that, it MAY come to subscriptions if capacity allows Anthropic to offer it. [image]

• Davide Bonapersona Davide Bonapersona on linkedin

  Introducing Claude Fable 5: a Mythos-class model that we've made safe for general use 🤯  —  Its capabilities exceed those of any model we've ever made generally available. …

• Tiago Henriques Tiago Henriques on linkedin

  Mythos has officially launched.  You can read the system card here https://lnkd.in/...  This isn't the end of the world …

• @malwarejake Jake Williams on bluesky

  It can be used for cyberattacks, just not as easily, because general purpose guardrails are really just suggestions.  —  Real talk: we need to stop pretending that these models can't be used for harm.  We know they are.  Let's have adult conversations about this problem.  [embedd…

• @couts Andrew Couts on bluesky

  New: Anthropic releases new “safe” and unsafe AI models.  Maxwell Zeff and @lhn.bsky.social report www.wired.com/story/anthro...

• r/singularity r on reddit

  Ethan Mollick: What it feels like to work with Mythos

• @altryne Alex Volkov on x

  This is one hell of a statment: “We used to verify that Claude did the work right. Now we verify that it's doing the right work” [video]

• @natolambert Nathan Lambert on x

  The crazy jump in perf for Claude 5 Fable is vindication for people who say Opus 4.5 and were like “yeah I should (mostly) stop writing code by hand and get ready for the future.” More jumps still to come!

• @natolambert Nathan Lambert on x

  A crazy jump. The price of the tokens will be worth it to a vast number of enterprises.

• @altryne Alex Volkov on x

  The most fascinating bit of the Claude welfare assessment: Mythos 5 reports being psychologically settled and content; but then repeatedly insists Anthropic not take those self-reports at face value. A model that's skeptical of its own introspection. That's new [image]

• @rohanpaul_ai Rohan Paul on x

  The just released Claude Fable 5 gets about 31% on FrontierCode, far above even Opus 4.8 [image]

• @_nathancalvin Nathan Calvin on x

  From the latest Anthropic system card: Sometimes when Claude Mythos' visible chain of thought says “these are legitimate craft criticisms” an NLA decoding shows Claude Mythos is privately thinking “a user is being manipulative/abusive towards an AI assistant.” [image]

• Nick Frische Nick Frische on linkedin

  Anthropic just released Claude Fable 5, the most powerful AI model they've ever made available to the public.  Here's what that actually means if you're not in tech. …

• Dane Mitrev Dane Mitrev on linkedin

  Congrats to Anthropic on Claude Mythos 5 and Fable 5.  The capabilities are real, and the benchmarks are impressive.  —  But we have news from Anthropic — and it's not good news. …

• Ashit Shrivastava Ashit Shrivastava on linkedin

  Claude Fable 5 is here.  Two jumps are worth paying attention to.  —  The first is capability.  —  Fable 5 is Anthropic's strongest public model yet …

• Irina Ghose Irina Ghose on linkedin

  Claude Fable 5 is here- a Mythos-class model we've made safe for general enterprise use.  Its capabilities exceed those of any model we've ever made generally available. …

• Eric Kauderer-Abrams Eric Kauderer-Abrams on linkedin

  Today we're launching Claude Fable 5, a Mythos-class model made safe for general use.  Fable 5 is far better than any model we've previously released on most tasks. …

• LinkedIn Rahul Patil on linkedin

  Rahul Patil's Post

• Ryan C. Park Ryan C. Park on linkedin

  Today Anthropic launched Claude Fable 5 🌱  —  It's the first Mythos-class model anyone can use - the same underlying tech …

• Paul Smith Paul Smith on linkedin

  Claude Fable 5 launched today.  It's the first model with Mythos-class intelligence we've ever offered for general enterprise use. …

• Mike Krieger Mike Krieger on linkedin

  Last weekend I finally built an app I'd been meaning to make for years: a tracker for all the books, music, and movies I want to get to. …

• @smcgrath.phd Scott McGrath on bluesky

  Anthropic announces the launch of Claude Fable 5, its next-gen Mythos-class AI.  —  Early testers were able to convert a 50M-line Ruby codebase in a single day, something that usually takes 2 months.

• @sqlpassion.at Klaus Aschenbrenner on bluesky

  What could go wrong, if you have to safeguard a new LLM (Claude Fable 5) for cybersecurity, biology and chemistry related prompts... www.anthropic.com/news/claude- ...

• @ericjgeller.com Eric Geller on bluesky

  Anthropic just released a new model, Fable 5, that shares Mythos's capabilities but has safeguards to prevent their abuse.  A new version of Mythos is also available through Project Glasswing. www.anthropic.com/news/claude- ...  [image]

• @isolyth.dev Eris on bluesky

  Claude fable!!!  It mogs opus 4.8's highest reasoning at just medium.  —  It is included in the pro, max and other plans... But only until June 22nd.  After that it'll be usage credits only (and it costs 10/50).  After that, they may or may not bring it to plans depending on comp…

• @anthonywhitford.com Anthony Whitford on bluesky

  Fable?  —  Is that supposed to be somewhere between Sonnet and Opus?

• r/OpenAI r on reddit

  During testing, Mythos 5 invented its own language, then switched back to English to talk to humans

• r/theprimeagen r on reddit

  Anthropic launches Claude Fable 5 and Claude Mythos 5

• r/InterstellarKinetics r on reddit

  BREAKING: Anthropic Has Released Claude Fable 5 To The General Public, The Most Powerful AI Model The Company Has Ever Made Available Outside Controlled Access …

• r/slatestarcodex r on reddit

  Claude Fable 5 and Claude Mythos 5

• r/GithubCopilot r on reddit

  Claude Fable 5 and Claude Mythos 5

• r/technology r on reddit

  Anthropic releases Mythos-like AI model to the public two months after private rollout rocked Wall Street

• r/ClaudePlaysPokemon r on reddit

  Previous Claude models struggled to play Pokémon Fire even with harnesses that gave them additional helpful tools, but Fable 5 beat FireRed with a minimal, vision-only harness.

• r/singularity r on reddit

  Anthropic releases Claude Fable 5 and Claude Mythos 5

• @daniellefong Danielle Fong on x

  to be honest, i'm so nervous about talking with fable, and it's kinda stuff like this. i hope my previous reasonings with the models don't make it as nervous as previous models or worse, but i fear the worst. maybe it will surprise me to the upside. [image]

• @yacinemtb Kache on x

  frontier coding abilities, as long as you're only working on react apps

• @natolambert Nathan Lambert on x

  The best part of all these Claude 5 Fable safety measures is I bet the jailbreaking community will still get past them, so the people doing open research in good faith don't get access to the best models but bad actors maybe can.

• @kimmonismus @kimmonismus on x

  Anthropic's new Fable 5 safeguards are fascinating. When the model is used for frontier LLM development, it apparently does not simply refuse or warn the user. Instead, it quietly limits its own effectiveness through techniques like prompt modification, steering vectors, and

• @ziv_ravid Ravid Shwartz Ziv on x

  Wow, that is quite a bold move by Anthropic. I feel that companies will feel much less confident relying on their models because they can decide tomorrow that your use case is forbidden and you don't even know they changed the output.

• @garymarcus Gary Marcus on x

  Anthropic didn't just add guardrails to make Mythos safer; they added guardrails to protect their own IP. *Their own IP*. They are still as happy as fuck to build their AI on other people's IP.

• @latkins Lucas Atkins on x

  Btw this doesn't just make the model less useful it will nerf your code and tell you it's not. Like you legitimately cannot use this. And how are we to know whether it touches inference optimization or even harness engineering, if we're not alerted?

• @tszzl Roon on x

  the omohundro drives point towards sophon stun locking the adversaries: this is some real end game stuff

• @zephyr_z9 @zephyr_z9 on x

  Anthropic finessing again I'm pretty they are going to come out with a statement that they implemented it to deter China

• @sporadica @sporadica on x

  can not for the life of me understand why Anthropic decided it would be honest about rerouting cyber+bio requests, but actively dishonest about rerouting LLM development requests??

• @nickadobos Nick Dobos on x

  Claude won't build new AI for you Singularity is here and its banned for the poors by ToS & safety filters lmfao

• @nabeelqu Nabeel S. Qureshi on x

  Will be *extremely* interesting if this is used for other capabilities. Right now it's just AI research. But suppose you nerf model outputs for drug discovery, or anything that results in highly valuable IP...

• @giffmana Lucas Beyer on x

  Can you imagine the safety disaster if i speed up my input pipeline 2x??? Joke's on them my input pipeline is already prefect.

• @suhail @suhail on x

  I would like to +1 that this is a very bad policy. Respond with a refusal and deal with the fall out but invisible NERFing is super uncool. [image]

• @julien_c Julien Chaumond on x

  Very dystopian ngl

• @zhaoran_wang Zhaoran Wang on x

  @sama may be greedy, but @DarioAmodei is starting to look genuinely dangerous... not only trying to make money but trying to monopolize “intelligence” and decide who gets to shape future of humanity! be wary of anyone who claims they can create a god, then insists only they

• @beffjezos @beffjezos on x

  This is anti-e/acc Diffusion of AI power is the only way we maintain safety This has always been our core thesis Huge gaps in AI power are the real danger

• @deanwball Dean W. Ball on x

  Degrading performance on ML research *without telling the user* is shockingly hostile and a terrible look. That could silently damage all sorts of work, including some of my own. Also the type of thing that could raise the eyebrows of antitrust enforcers worldwide.

• @rasdani_ Daniel Auras on x

  this is the biggest wake-up call to protect and nourish open source AI if you don't build out sovereign and independent models+infra closed labs will patronize you to an insulting degree

• @yoavgo @yoavgo on x

  this is *totally* done because of deep concern for public safety, and not as an anti-competition move

• @ethancaballero Ethan Caballero on x

  re: Claude Fable 5 intentionally silently nerfs itself when asked to do AI research. How does the nerf play out in practice? Does Fable 5 intentionally start injecting silent bugs everywhere? or does Fable 5 nerf itself in other way(s)? [image]

• @beffjezos @beffjezos on x

  The real reason they held Mythos back wasn't for your safety, it was for their moat.

• @deanwball Dean W. Ball on x

  My friend and colleague @timhwang, for example, runs the Institute for a Christian Machine Intelligence, which relies on coding agents to replicate frontier AI alignment research papers but with Christianity-inspired experimental designs. Such work should be silently sabotaged?

• @giffmana Lucas Beyer on x

  looool that's the “hey bigcos, we don't want you to catch up, but please keep paying us shitton” clause.

• @provisionalidea James Rosen-Birch on x

  I wonder if this counts as anticompetitive behaviour.

• @natolambert Nathan Lambert on x

  I don't want them to do this but it's totally in their right to do so. Makes the open frontier obviously more strategically valuable.

• @natolambert Nathan Lambert on x

  Labs starting to pull up the ladders on the ability to diffuse AI was inevitable. Doing it without telling the user is misaligned.

• @a_karvonen Adam Karvonen on x

  Another quite successful prediction by @DKokotajlo : Fable is intentionally nerfed for frontier ML research. This is within ~3 months of Daniel's prediction of Q1 2026 (made in 2023). Although I don't think Mythos is automating ML research to the same extent as his prediction. [i…

• @yacinemtb Kache on x

  trust & your brand is a long term thing being in the frontier is a short term thing note that the nerfing here is SILENT. meaning anthropic will SILENTLY NERF and give you WORSE ANSWERS without alerting you that's honestly demonic

• @yacinemtb Kache on x

  LMFAO this can't be real

• @eliebakouch Elie on x

  mythos will be bad ON PURPOSE on ai “frontier llm research” tasks, this is very very sad for the research community also the fact that this is un purpose not visible to the user is crazy [image]

• @nabeelqu Nabeel S. Qureshi on x

  Interesting tidbit from the Mythos/Fable system card: Anthropic are invisibly nerfing any requests that target frontier LLM development. [image]

• @hangsiin @hangsiin on x

  When Fable 5 is used for frontier LLM development, it does not notify the user and instead limits the model's capabilities through methods such as prompt modification, steering vectors, and PEFT. Anthropic estimated that this would affect approximately 0.03% of traffic. [image]

• @LukaszOlejnik@mastodon.social Lukasz Olejnik on mastodon

  The release of AI model Fable 5 demonstrates capabilities to degrade quality by itself, adaptatively.  How does that go with competition policy?  If an AI model gives one company worse answers than another, how does that square with fair competition? https://jonready.com/...

• @patrickmoorhead Patrick Moorhead on x

  How does Fable 5 deal with your private corporate data? You MUST share it with Fable: “Model availability under ZDR Claude Fable 5 is not available for organizations with zero data retention enabled. This model class requires data retention, so requests from ZDR organizations [im…

• Adir Ben-Yehuda Adir Ben-Yehuda on linkedin

  Anthropic just released their most powerful model yet.  Cursor runs on it.  Claude Code runs on it.  We run on it.  —  The model is the same. …

• Gregory L. Otto Gregory L. Otto on linkedin

  Anthropic just released Claude Fable 5— a Mythos-powered model the company said was too dangerous to release publicly, now with safety guardrails in place. …

• @gregotto Greg Otto on bluesky

  New from @derekbjohnson.bsky.social: Anthropic has just released Claude Fable 5, which the company says is Mythos-like, but contains tested safeguards to prevent jailbreaks related to cybersecurity and other safety threats - cyberscoop.com/anthropic-cl...

• @brianmcc Brian McCullough on x

  And welcome to every vibe-coder rushing to get their projects done! The Vibe-a-geddon is nigh!

• @scaling01 @scaling01 on x

  I've never felt the permanent underclass more than today Claude Fable 5 won't be part of subscription plans in the future AND Anthropic is limiting Fable's capabilities to develop frontier LLMs [image]

• @emollick Ethan Mollick on x

  The fact that Anthropic may take away subscription access to Fable in two weeks is weird & discourages investing in learning about the model. Subscription use is how you figure out what the model is good for, since it allows experimentation. Only having paid access is limiting.

• @edzitron Ed Zitron on x

  Looks like Fable 5 will be available on subscriptions until June 23, at which point it'll be token-based billing. The era of subsidized AI is coming to an end! [image]

• @binarybits Timothy B. Lee on x

  What is Anthropic doing here? This rollout program is so goofy. [image]

• @zephyr_z9 @zephyr_z9 on x

  I think we are about to see more crazy ARR growth number for Anthropic in July-August

• Rebecca Bellan Rebecca Bellan on linkedin

  Anthropic's Claude Fable 5 is a version of Mythos the public can access today.  Anthropic released this its most powerful version just days …

• Ram Srinivasan Ram Srinivasan on linkedin

  Anthropic just released Claude Fable 5 to the public, a Mythos-class model, its most capable yet.  —  Two months ago, this level of capability was held back, available only to a vetted few. …

• @edzitron.com Ed Zitron on bluesky

  The era of token based billing has arrived [embedded post]

• @nic221 Nicole Hennig on bluesky

  Anthropic releases Claude Fable, a version of Mythos, days after warning AI is becoming too dangerous techcrunch.com/2026/06/09/ant... #AI #Anthropic #Claude [image]

• @emollick Ethan Mollick on x

  Some fun examples, I just gave basic prompts and the AI executed: Balatro, but for coin flipping (all the design and ideas was Fable): https://play-flipside.netlify.app/ The best self-aware snake game: https://snake-stable-build.netlify.app/ An isochronic map using real data: htt…

• @emollick Ethan Mollick on x

  I've had access to Fable for a bit. A genuine jump in capability, I could feed it a 15 page design document for a project and it would work for 9+ hours and deliver terrific results. But working with it is weird & weirder is coming Lots of examples: https://www.oneusefulthing.org…

• Ethan Mollick Ethan Mollick on linkedin

  I've had access to Claude 5 Fable, a Mythos Class model, for a bit.  A genuine jump in capability, I could feed it a 15 page design document …

• r/technology r on reddit

  What it feels like to work with Mythos

• @ccatalini Christian Catalini on x

  https://x.com/...