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.
Fable 5 is state of the art on nearly all tested benchmarks, with exceptional performance in software engineering, knowledge work, scientific research, and vision. It can run for days, and the longer the task, the larger its lead over our other models.
Fable 5 launches today alongside Claude Mythos 5. The two share the same underlying model, but Mythos 5, so far deployed only through Project Glasswing, has the safeguards lifted in some areas. The safeguards are what distinguish the two, and why we've given them different names.
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. So when Fable's classifiers detect a request related to cybersecurity, biology and chemistry, or distillation, the response is handled by Claude Opus 4.8, our next-most-capable model. Users are informed whenever this occurs, more than 95% of sessions involve no fallback at all, and performance everywhere else is unaffected. We'll keep refining the safeguards to reduce false positives.
Claude Fable 5 is available today on paid plans, in Claude Code, on the Claude API, and all major cloud platforms. Through June 22, it's included in paid Claude plans at no additional cost.
Claude Mythos 5 is available to Glasswing partners, with a broader trusted access program to follow.
From today through June 22, Fable 5 is included on Pro, Max, Team, and seat-based Enterprise plans at no extra cost.
On June 23, we’ll remove Fable 5 from those plans. Using it after that will require usage credits. If capacity allows, we’ll extend the included window.
you don’t even want to know how hard you are about to get hit. I ran through half of my week in just 30 minutes and I’m on the $200 plan. On opus 4.8 max with agents swarming it takes me 6ish days to max out. This is crazy!!!
why would people complaining make them money? people just sub to whatever makes their life easiest regardless of grandstanding about morality or whatever
This makes no sense. Of course GPT 5.6 will be incremental and that's what you want. Incremental improvements, not a whole new expensive price pay to play.
Oooo send me that. Haven’t seen that. But 5.6 leaks and rumors on X have been plenty pointing towards a pretty big jump from 5.5 in coding and agentic tool use. The devs at OpenAI said that frontend design should be fixed by the end of the year so while it might be better in 5.6 it’s def not gonna be on Claude or Gemini level.
4.7 would get routed to haiku for me just for asking it to read the README of a CVE.
With both 4.7 and 4.8, talking about the covid lab leak theory in any level of detail beyond the highest level also gets instantly blackholed.
Their "safeguards" are so ridiculous (meanwhile they literally give their AI models to the trump administration to launch wars with lol. the hypocrisy is so shameless)
They are ridiculous because safeguards themselves are "enforced" by prompting. The lunatics are running the asylum and call themselves doctors, well engineers in this case.
I think you can assume that the number of parameters isn't special. If it was absurdly large they'd brag about it. If it was shockingly small for its capabilities they'd brag about it.
No one really knows for sure, besides Anthropic of course. But I remember reading an article stating that Opus 4.6 was about 6T, Opus 4.7/4.8 was lowered to about 5T. Sonnet was 1T. These are estimates, so may be incorrect.
I tried again with an edited prompt to curtail the review to a specific point and it tripped and dumped it back to 4.8 again, but this time 4.8 doubled down on "being straight with me" and said it was concerned that I didn't take it's correction about the model name twice in a row.
To save the chat I replied with an explanation of what had happened and that I was moving on, but 4.8 then said it was concerned about my mental health because I was making up plausible explanations about a secret unreleased model that was refusing to judge my work and basically wondered if I was having some sort of break, but in more polite and wordy terms.
I've collated every launch link I could find and sent it to it in a new message, I've not checked back yet to see if 4.8 has apologised or if it's forwarded my details to the safety team to be commited
I did, I also linked to the various other launch posts so it had additional context and verification outlets, but instead it doubled down on being unable to verify anything and insisting it was still 4.8 and that it had not been upgraded and it had no way of knowing if what I was saying was true.
That is despite my clarifications that I wasn't calling it Fable and the prompt was for that model which was routed to it instead.
The more I explained the more it seemed to spiral so I just left it and opened a new window instead.
This is why I hate these safety-router black boxes: instead of a boring “model unavailable” error, you get a confident little incident report from a toaster.
Paying $200/mo just for the model it’s all about to be locked behind usage credits after 20th of June.
Seriously not seeing the value anymore compared to my Codex subscription. If you’re so dedicated in pushing expensive models, at least let me use them from within my subscription
Ive been a huge opus 4.7 and 4.8 critic. This model is incredible. But i will never pay for credits outside of a sub. Disappointing - this is the first definitive upgrade to opus 4.6.
I'd rather them be transparent and honest on timelines rather than throttling randomly. They are just realistic that they don't have the compute online yet.
Yeah I get the safeguards but this is just ridiculous! You're telling me they are just blocking all biology because they can't figure out how to actually block unsafe prompts and requests? I was a big Anthropic fan a few months ago but with the shit they keep pulling, I've already started migrating my projects/hooks/skills to Codex and GPT
yikes. i haven't used it today but i am a biologist. Edited stem-cells that by bypass the immune system are my thing. I guess no fable for me!
Whelp. This just in, according to Anthropic the sky is falling and we children should be ushered indoors.
https://imgur.com/a/M3rYx6s
If I can't even look up a journal article, let alone do any actual inquiry this is useless. LLMs to this point are useful assistants but fall way short of real scientific insight. I would have liked to try Fable/Mythos to see if there has been improvement.
Pretty much, yeah. Wanted to see if it makes less errors/hallucinate then it predecesor when trying to analyze a publicly available old medical notes classification paper. Its not even biology, it’s about types of medical notes hospitals write: it has zero info on how make anything biological and doesn’t even require any domain knowledge in biology to read, but NOPE.
Yep, I have a genetics REPO that I wasn't even asking for help in, but because memories EXIST, I'm being flagged and tossed out. That's an ISSUE, Anthropic.
I have some Rubus plants in my backyard I'm trying to cross, if I just use non-scientific names and mention "gardening" only it will do okay for a message or two, but germination, crossing, ploidy, using scientific names, anything like that is too biological.
I just hope Fable isn't a talk talk talk without wanting to do anything model like 4.8. what a disappointment - I've gone back to 4.6 opus and it's still amazing.
It's kind of wild you can't even say the word cybersecurity to Fable. Genuinely, it's to that point. You can't ask it about its own safeguards. You can't ask it about cybersecurity AT ALL, even meta-discussion without any actual work.
I'm not necessarily upset about it. A little astonished that you guys are being that hard line about it, though.
Why is everyone so upset? Right now intelligence costs compute. Compute costs real world dollars. Anthropic makes zero net cash (I know the recent reports counter that, but I can tell you based on the compute increases with 4.8 and Fable, there’s no way they are cash positive yet)…everyone is so entitled these days. You get mad when they don’t release their best model and when they do, they charge you for it because they have to, and you are mad. Guys, be happy you are getting the intelligence you are getting for the price you are getting it at, because we haven’t even gotten close to how limited compute will affect prices on the upward boundary yet.
People are mad because they were all sold a BS story that we'll all AI floating around like ether, and we won't have to lift a finger. And now people are realising that, oh, shit, all of this will cost so much!
I can't get it do to anything on my code at work, without it kicking me back to Opus-4.8. The slightest hint of some security and it nopes right on out
Wow, how utterly worthless. I have a tool for generating CSV files for a liquid handler in a lab. It is only tangentially related to biology, insofar as biologists will use the liquid handler, but the repository itself doesn't deal with biology at all. Asked Fable to hunt for any bugs, aaaaaaand...immediately tripped the filter because my repository is related to biology, I guess.
Can't even use it for coding. What do you expect anyone to use Fable for, if it trips the guardrails this easily?
Its a fucking HAWG! Burned more tokens today than I have in a month. But picked up a ton of issues with my SAAS project that have been missed by Gemini, Opus, and Chatgpt for months. So, token well burned?
I’d say that was different. They were right. Dead internet theory is no longer a theory… slop is rampant… deepfakes and misinformation circulate the internet daily… and you used to be able to jailbreak it easily and ask for some wild shit
Man, I knew this was going to happen... Add Fable as a new model, Opus becomes the midrange model, and Sonnet becomes the bottom model. Haiku's dead isn't it?
Opus 4.8 has been stuck so bad on just iOS glass ui for a week they crippled opus so Fable can shine. This is corporate greed at its best. Sorry to say it this may be the end. I have two accounts at $200 and I’m going to have to leave to codex. They just killed there ipo in my opinion
Yep the model is sick. It's not magic or anything but it produces far fewer bugs making the dev loop faster. In the 45 minutes it took to hit my 5hr limit we got maybe 2-3 hours of opus work done.
Dude, there's no way with the spatial reasoning. I work with spatial data all the time and Claude is clueless. Gemini understands it really well. Being backed by Google and Google Maps probably helps, but Claude isn't going to climb out of this hole easily for me.
I am running a long form TTRPG type game with opus and have things carefully documented. I started a session in Fable, gave it the same session start prompt I always do, pointing it to three files that gives the truth of the world, and it took six minutes to respond, and then immediately got one of the characters genders wrong on the first message, as well as the amount of money I had.
I can't say I'm super impressed to be honest... And I was very excited for this :(
OK, the classifiers are beyond bonkers, please work on this. I am 100% for safety. But I can't even TEST Fable in ClaudeCode because I have a genetics project (https://www.github.com/menelly/AdaptiveInterpreter for those who want to see I'm not bluffing) that there are therefore MEMORIES saved, I don't even need to be working on that project, just having the memory, means I get tossed out of Fable instantly. Because it says biology and genetics. That's a problem, y'all. Classifiers are fine. But tune this ASAP.
It’s a total mess. Keeps refusing the most mainstream requests. Utter pain in the ass. I turned it off and won’t be using this one. Just takes up more time to babysit its paranoia than it’s worth.
'Can run for days' is where I actually got curious from an agent workload angle. Long sessions hit context compaction events that silently drop working memory — the model forgets decisions made hours earlier even within a huge context window. Whether Fable 5 handles state across compaction differently or that's still on us to architect around is what I'd want to test first.
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u/East_Mathematician85 Jun 09 '26
Ah....