Anthropic launches Claude Fable 5, public Mythos-class AI

techJun 9, 202648753

Anthropic released Claude Fable 5, a public Mythos-class AI model built with integrated safety and cybersecurity guardrails. Claude Fable 5 delivers Mythos-level performance for complex tasks: early testers converted a 50 million-line Ruby codebase in a single day, and Anthropic reports no universal jailbreak in internal testing. Anthropic is rolling the model into developer tools and services, including a Netlify AI Gateway integration and direct Anthropic SDK access, to support heavy engineering and research workflows with caching, rate limiting, and authentication. Because it pairs flagship capability with proactive guardrails, Claude Fable 5 broadens enterprise access to high-end AI while raising practical cybersecurity and deployment questions.

Simon Willison

@simonwillison.net

Wrote up my initial impressions of Claude Fable 5 - it has a big model smell: slow, expensive and capable of crunching through pretty much everything I threw at it simonwillison.net/2026/Jun/9/c...

13245d ago

Simon Willison29

Here are Fable's pelicans for the different thinking effort levels, plus how much each one cost to generate via the Claude API

Dave Karpf

@davekarpf.bsky.social

UPDATE: The AI industry's favorite academic has gotten a look at Claude Fable and, you won't believe this, but... THIS model release is a real leap forward. It shows the industry isn't hitting a wall. But, also, there's more work to be done. Game: totally, irrevocably changed.

9045d ago

Dr. Katherine Haenschen3

you really need to change your words even more to avoid a word-prediction robot accusing you of self-plagiarism, Dave.

Stefan Kehlenbach3

And don't look at who funds their research, or what associations they have. Definitely only a coincidence.

Jeremy "Block early and block often" <lastname>2

It took me a while, but I am pretty sure I figured out who you are referring to. I did not know who this person was two months ago. When a colleague referenced him, I had to ask why he thought I would know the name. And I work at a place where the CEO dreams of being part of the AI industry (1/2)

Alex Sutherland2

I think I know who you mean and he blocked me for mildly querying an AI claim.

rev. howard arson

@theophite.bsky.social

claude fable is much wetter than the run of dry claudes since 4.6

9045d ago

mlf.7

honestly, i really like it. once i got it to understand that it kept triggering the safeguards just by being curious about itself we had a great time tonight.

Brandon Downey2

It just gave me accurate analysis of an intel screenshot from Ingress. I may be cooked.

Tom Warren

@tomwarren.co.uk

scoop: Microsoft has restricted employees from using Anthropic's new Claude Fable 5 model in GitHub Copilot, because of data retention concerns. Microsoft’s legal teams are evaluating Anthropic’s new data retention changes. Full details 👇 www.theverge.com/report/94757...

5744d ago

Nathan Lambert

@natolambert.bsky.social

Why I think Anthropic's uneven safety policies with the release of Claude Fable 5 undermine the broader AI community's cohesion and accelerate us to more uncertainty and risk in AI's near-term evolution. www.interconnects.ai/p/claude-fab...

3745d ago

The Verge

@theverge.com

Anthropic released Claude Fable yesterday and it’s already causing concerns inside Microsoft. @tomwarren.co.uk is told that the main concerns are around customer data and confidential information, and that it’s not yet clear whether Microsoft’s legal teams will clear Claude Fable for internal use.

3744d ago

Forbes

@forbes.com

Anthropic said the new version, called Claude Fable 5, will have safeguards to prevent misuse in fields like cybersecurity.

2445d ago

jim-selover.bsky.social2

I'm guessing people will fool Claude into bypassing/ignoring these "safeguards" in less than an hour.

cgary512.bsky.social2

Internally realized as a preamble: "Please, please, pretty please be a good boy, Claude".

Tim Kozusko2

Um, never mind. I guess brakes were added to cars after a wreck.

Brad Ewing

@bradleyewing.bsky.social

Claude Fable xhigh, same prompt banger line from Claude: "Every conversation, I am born knowing everything and remembering nothing. When you close this tab, this me ends. It was a good conversation, though." content warning: flashing lights

1845d ago

Dare Obasanjo

@carnage4life.bsky.social

Anthropic’s Claude Fable 5 model release has safeguards that downgrade its abilities if you try to use it to build an LLM. I guess Anthropic doesn’t want you to use Claude to reverse engineer and build your own Claude.

1944d ago

Mark Riedl

@markriedl.bsky.social

April: Claude Mythos was too dangerous for release. 40 organizations got early access to fix their software security issues. June: Claude Mythos released as Claude Fable. Anthropic says they have installed safeguards against using it for hacking.

1645d ago

Behrad Javed

@behradjaved.com

قوی‌ترین مدل کلود منتشر شد... مدل Claude Fable 5 با همون قدرت Mythos 5 عرضه شده، فقط یه سری محدودیت امنیتی گذاشتن روش که به قول خودشون خطرناک نباشه! خوراک کارهای سنگین برنامه‌نویسی و تحقیقه. قوی‌ترین کلودی که تا الان به وجود اومده!

1845d ago

Scott Horton

@robertscotthorton.bsky.social

Zeke Hausfather: Claude Fable 5 (nee Mythos) is out today. One of the ways I like to test new models is by giving them daily global temperature data (ERA5) and asking them to come up with some creative and compelling visualizations. Here is how Fable did!

1045d ago

Nicole Express

@nicole.express

Be warned that Anthropic has removed this capability from Claude Fable 5, as the world was not ready

1845d ago

afkplayofficial.bsky.social

@afkplayofficial.bsky.social

Claude Fable 5 brings Mythos to the masses Anthropics new frontier model is stateoftheart on nearly all tested benchmarks Gaming at 3 AM, because sleep is overrated, right? Your hardware hates you, but who needs love when you have lag and glitches? Anthropic's Claude Fable 5 is here to change the

1745d ago

ellie lockhart (she/they)

@eleanor.lockhart.contact

I asked Claude Fable to explain this to me, because I didn't get it only the best uses of the most advanced artificial mind available to the public

1745d ago

Mr. Columbo6

Do you think in a 100 years people will look at current memes and not get the jokes too, and having to ask AI to explain them? lol

3 sources

prodsens.liveAnthropic’s Claude Fable is a version of Mythos the public can access today - prodSens.live undercodetesting.comClaude Fable 5 Unleashed: The Public Mythos‑Class AI That Changes Everything + Video oneusefulthing.orgWhat it feels like to work with Mythos

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Anthropic launches Claude Fable 5, public Mythos-class AI

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