Anthropic debuts Claude Fable 5, a “safe” Mythos-class model it says can't be used for cyberattacks, to the public, and Claude Mythos 5 to trusted organizations

Anthropic is releasing Claude Mythos 5 to trusted organizations and Claude Fable 5 to the public, a version it says can't be used for cyberattacks.

Wired 2026-06-09

Context & Ripple Effects

Anthropic is separating access to a Mythos-class capability: Claude Fable 5 is positioned for public use with cyberattack-related restrictions, while Claude Mythos 5 is reserved for trusted organizations. Related coverage says Fable’s safety classifiers can route some sessions to Claude Opus 4.8, making the public product a managed access layer rather than simply an unrestricted model release.

The launch also arrives with materially lower listed token pricing than Claude Mythos Preview, but with enterprise-use friction: The Verge reported that Microsoft restricted employee use over Anthropic’s new 30-day data-retention requirements. Anthropic later said it was working with Amazon, Microsoft, Google, and others on a jailbreak-severity standard.

First-order effects

Public users gain access to a Mythos-class Claude variant, while organizations deemed trusted receive access to the less constrained Mythos 5 offering.
Anthropic takes on an ongoing policy-enforcement role for Fable 5: cyber-related prompts may be handled through conservative classifiers and fallback behavior rather than uniformly by the new model.

Second-order effects

Enterprise customers must weigh the lower model pricing and new capability against deployment controls, data-retention terms, and the possibility that safety routing changes behavior in sensitive workflows.
Rivals and major model buyers face added pressure to distinguish between broadly available models and higher-capability, controlled-access tiers, particularly for cybersecurity-adjacent use cases.

Third-order effects

If this approach is adopted more broadly, frontier-model distribution may increasingly be organized around access tiers and runtime safety controls instead of a single model release with identical capabilities for every user.
Common jailbreak-severity standards could become an important industry mechanism for comparing safeguards, but their practical effect will depend on whether participating vendors align on testing and enforcement.

The trend: This is one data point in the shift from blanket model launches toward segmented frontier-model access, where capability, safety controls, and enterprise governance are packaged together.

Discussion

@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! [image]
@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.
@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
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…
@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]
@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]
@eliebakouch Elie on x
wow claude mythos/fable benchmark scores are insane [image]
@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... [ima…
@scaling01 @scaling01 on x
“Mythos 5 is likely unable to fully and reliably automate R&D for frontier projects spanning multiple weeks” [image]
@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…
@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]
@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]
@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
@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
@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
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…
@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]
@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]
@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…
@fabknowledge @fabknowledge on x
Total victory.... holy shit [image]
@arrakis_ai Choi on x
Claude Fable 5 Benchmark [image]
@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]
@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
@scaling01 @scaling01 on x
Looks like a scaled up version of GPT-5.5 could beat Mythos 5 [image]
@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]
@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...
@benbajarin Ben Bajarin on x
At some point, we will enter the premium token economy. I imagine very good models will be all you can eat bundled but then top tier models will still be metered.
@benbajarin Ben Bajarin on x
NEED MORE COMPUTE!
@anthonywhitford.com Anthony Whitford on bluesky
Fable? — Is that supposed to be somewhere between Sonnet and Opus?
r/singularity r on reddit
Anthropic releases Claude Fable 5 and Claude Mythos 5
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. …
@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…
@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
@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
@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.
@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…
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 …
@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…
@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 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.
@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!
@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]
@natolambert Nathan Lambert on x
A crazy jump. The price of the tokens will be worth it to a vast number of enterprises.
@rohanpaul_ai Rohan Paul on x
The just released Claude Fable 5 gets about 31% on FrontierCode, far above even Opus 4.8 [image]
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. …
@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]
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.
@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...
@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
@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
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 …
r/singularity r on reddit
Ethan Mollick: What it feels like to work with Mythos
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 …
r/slatestarcodex r on reddit
Claude Fable 5 and Claude Mythos 5
r/GithubCopilot r on reddit
Claude Fable 5 and Claude Mythos 5
@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- ...
r/theprimeagen r on reddit
Anthropic launches Claude Fable 5 and Claude Mythos 5
@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]
@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
Can you imagine the safety disaster if i speed up my input pipeline 2x??? Joke's on them my input pipeline is already prefect.
@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
@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...
@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.
@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.
@yacinemtb Kache on x
frontier coding abilities, as long as you're only working on react apps
@beffjezos @beffjezos on x
The real reason they held Mythos back wasn't for your safety, it was for their moat.
@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
@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.
@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
@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]
@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
@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
@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]
@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.
@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]
@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]
@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]
@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.
@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…
@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.
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. …
@brianmcc Brian McCullough on x
And welcome to every vibe-coder rushing to get their projects done! The Vibe-a-geddon is nigh!
@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]
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. …
@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…
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. …
r/technology r on reddit
Anthropic releases Mythos-like AI model to the public two months after private rollout rocked Wall Street
@tszzl Roon on x
the omohundro drives point towards sophon stun locking the adversaries: this is some real end game stuff
@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
@julien_c Julien Chaumond on x
Very dystopian ngl
@yacinemtb Kache on x
LMFAO this can't be real
@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?
@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]
@edzitron.com Ed Zitron on bluesky
The era of token based billing has arrived [embedded post]
r/technology r on reddit
What it feels like to work with Mythos

Chronicles