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Comments (218)

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  skeledrew
  Damn people were right about 5.5 being nerfed in preparation for a version release. This is not at all a good look.- https://news.ycombinator.com/item?id=50422069
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  yewenjie
  > Our first formalization of Fermat’s Last Theorem, performed by an unreleased research version of Claude, took 11 days. It relied on a purpose-built harness along with guidance from a human researcher. By contrast, a team of 1,000 Fable 5.2 agents fully formalized the theorem in just 30 hours, with minimal human intervention. Fable 5.2 started from minimal prompts, built its own ways to coordinate, and used no mathematical references, only a list of intermediate theorem statements to score progress. It needed one-third of the action tokens as our first formalization and produced a proof seven times shorter. As can be seen in the figure below, Opus 5.5 (with the same 1,000-agent setup) completed only 26% of the formalization in 18 hours, and barely made any more progress after 30.Most people don't really have intuitions on what it means to push the frontier now (because AI has surpassed everything they are good at, for example, coding). We are truly inside the singularity (using Kurzweil's definition, slightly paraphrased - the time when technology progresses so fast no one can keep track with it).
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  postalcoder
  I’ve had a chance to use fable 5.2. Some observations:- Anthropic is finally well balanced across models. Meaning: Opus 5.5 is so good that I do not feel Fable FOMO as I did when it was Fable 5/5.1 vs Opus 4.8/5. And Sonnet 5.5 sometimes makes me forget about Opus.- Fable is good, but you really have to push the ambition of your prompt in order to see proper separation from Opus 5.5. I personally have a hard time telling the difference between Fable 5.2 and Opus 5.5 for ordinary coding tasks.- It’s way faster and more reliable: one of the worst things about fable 5.1 was how slow it was an, on top of that, how frequently it would suffer from max output token overflows. I got none of these issues with 5.2.- Fable is exceptional at drawing. It’s ability to render an image with JavaScript actually has me questioning the value of dedicated image models. I prefer the images I’ve gotten fable/opus to make for me over those from gpt-image, it’s wild to think we’re at this point.
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  breakwaterlabs
  - Why are they stacking Fable xHigh against Carbon Med?- How did they produce such a bizarre effort-intel curve for Carbon that goes against every available benchmark?- Why did they leave Carbon-- positioned primarily as a cyber model-- off of the single cyber benchmark comparison?- Why do they switch to comparing against Argon (rather than carbon) for robodojo?
• phillennium
  Every time there's a flagship release like that, I wonder what simple "benchmark task" could I give it to see the the capabilities change in most obvious way, instead of trusting the official blog post.I'm not a mathematician to use Erdős problems for testing. I'm also not willing to spend buckloads of tokens just for a test. What is simple and quick but telling? What tasks are not saturated by previous models? Do you have a task you give new models?
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  dualvariable
  Setting aside the comments about nerfing, do normal mortals out there have workflows that really require Fable/Mythos and don't just work fine on Opus 5.5?I've been using Opus 5.5 on xhigh for some decently aggressive software development on a ~125k-line project, and it has been fine for me. I'm not really willing to dive into a "rewrite the whole project, don't make any mistakes" level of refactoring. I'm not looking to try to prove Fermat's Last Theorem myself. Is there anything that I'm truly missing?
• pacman1337
  I can't understand why people continue using opus 5.5. Significantly more expensive than other models that produce exact same results (for coding results only)If you are using Opus 5.5 I'm curious if it is because 1) your workflow is just stuck on it, 2) you don't care about money because you ain't paying it or 3 )do you think you get better results.If you 3 please let me know your experience and how you actually measure it, or if you just feel it is better.
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  cobri
  Does this coincide with the claimed nerfing of Opus 5.5? https://news.ycombinator.com/item?id=50422069
• advaith08
  We've been early testing Fable 5.2, and have been surprised by its coding ability. It was able to work with an esoteric 600k line fortran codebase to speed up some computational material science work for us by 36 times (!). Given that this could be done in 2 days, we've decided to open-source the results https://github.com/discovered-materials/dm_qe
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  __natty__
  Maybe it's just me, but I found Claude's writing style terrible compared to GPT or Gemini. It's "smart", but the way it communicates seems somehow off compared to other models.
• george_max
  https://www.youtube.com/watch?v=vdYynH177h0Seems like a new focus is electronics design, which is both interesting and a little sad to me. Manually designing electronics are one of the things I found incredible comfort in doing; seeing AI emerging in this space gives me mixed feelings.
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  minimaxir
  There were more than a few "leaks" saying it would be called Fable 5.5, so I'm curious if a) the leaks were just engagementbait or b) Anthropic changed it, despite the fact that Fable 5.2 being better than Opus 5.5 is confusing.Surprisingly the model is available immediately in my Claude Code: usually there's a delay, either for rollout or safety.
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  bhu8
  Ethan Mollick's take and early testing with Fable 5.2: https://www.oneusefulthing.org/p/fable-52-and-jagged-agi
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  pookieinc
  “Testers have found that Fable 5.2 and Mythos 5.2 communicate more clearly than past Fable and Mythos models. They generate outputs up to 30% faster than Claude Fable 5.1 and Claude Mythos 5.1, and they’re available at a lower price: $8 per million input tokens and $40 per million output tokens.”Honestly incredible that they’ve managed to beat all benchmarks, while making it cheaper. Always happy to see improvements offered at lower costs.Will be interesting to see what OpenAI does in response
• george_max
  Looking at Artificial Analysis index, the price is absurd to me.https://artificialanalysis.ai/GPT-6.1 Sol costs $1.27 per task, whereas Fable 5.2 is $26.54 per task -- a ~21x price difference.Fable 5.2 is not 21 times better than GPT 6.1 Sol, I find it hard to justify this.
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  jjcm
  Image to html comparisons of Fable 5.2 and Opus 5.5 (the previous SOTA for this test):Fable 5.2: https://html.non.io/lcars-fable-5.2/Opus 5.5: https://html.non.io/lcars-opus-5.5/Source designs: https://diffui.ai/app/canvas/5093e689-1e74-4f26-b632-2a4500f...Thoughts:The best implementation wrt being as true as possible to the source design. It nails the flowing svg shapes. Icons are more accurate to the design - note the difference between the starship svg in the "Legendary platforms" card between Opus 5.5 and Fable 5.2. The 3js planets outside the windows are also really well done, especially the bottom one which has a nice background glow to it.It isn't without issues though - the flicker effect it added to the S shaped svg that weaves through the page is distracting in my opinion, and I actually thing the motion animation in the Opus 5.5 one is better overall. Still, it nails the implementation of this page, but it's no surprise considering how good Opus 5.5 was at this.Disclaimer / reminder: the objective of this test isn't to have a well designed webpage, it's a synthetic test that pushes the limits of LLM's vision capabilities. Traditionally LLMs have issues with smooth curves, svg animations, and non-boxy layouts, which this design pushes the limits of.
• unshavedyak
  Looks like some plans get extra fable usage: https://support.claude.com/en/articles/17506494-claude-fable...
• stefanpie
  This part is mega concerning to me as someone who researches AI for hardware accelerator design and EDA: Safeguards AI research and development. The model that underlies Claude Fable 5.2 and Claude Mythos 5.2 is a step forward in general capabilities. However, during the model’s training, we took steps to limit advances in the specific research capabilities that could most directly accelerate AI development. Thus, in relevant areas, including accelerator kernel optimization and improving large language model architectures, Fable 5.2 and Claude Mythos 5.2 perform at about the level of Opus 5.5. Importantly, we ensured that the training changes did not affect related capabilities like agentic coding, hardware development, and traditional AI or machine learning research (including interpretability research). We do not alter these capabilities as the model is being served to users (that is, at inference time). As described in Section 1.5 of the system card (https://www.anthropic.com/document/claude-fable-5-2-mythos-5-2-system-card) and similarly to previous models, Fable 5.2 and Claude Mythos 5.2 also include transparent fallbacks to Opus 5 for a small set of topics in this domain, including kernel development on certain nonstandard accelerators. They are starting to deliberately limit public access to certain AI capabilities related to computer architecture and hardware optimization.To be clear, they explicitly say they are only targeting very specific capabilities, like accelerator kernel optimization, and that broader hardware development capabilities are unaffected. But 1) even that is pretty bold, especially the part about kernel development for nonstandard accelerator architectures, and 2) I worry that this could eventually expand to more areas of comp. arch., high-level digital design, chip design, and EDA.My speculation is that, as these kinds of chip design and EDA capabilities become increasingly important to frontier AI labs and their competitive advantages, there will be more incentives to restrict them.I don't think they've explicitly stated anything like this before regarding restrictions on these specific capabilities, but I could be wrong.
• lacoolj
  Yet Opus 5.5 is only a few % under all of these benchmarks (cept the robotics and labor ones)Do we need new benchmarks or are the models just plateauing in general? Or is it something I just don't see?
• moecables
  They're adding 1 to 3 resets for Fable only for all paid accounts. My work's Claude Max got 2 resets. My personal $20 plan got 1 reset.
• x187463
  I've very interested in the improvements to robotics control capabilities. This model was able to outperform specialized robotics models. It's the bitter lesson coming for robotics.
• damsta
  Nerfing Opus 5.5 was obvious signal that something new is coming and here we are. I appreciate the resets and lower API price though. Please add selective context compaction, it would probably take an hour max for you to implement it.
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  aurareturn
  Is this the Model 4 internal name?Reference: https://x.com/METR_Evals/status/2118412205662314935
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  bananaflag
  Those theoretical physics papers look like the real thing (i.e. not mathematical physics like the OpenAI Yang-Mills result). It looks like AI is finally branching out of math.
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  hmate9
  Its cheaper at $8 per million input tokens and $40 per million output tokens which is also pretty sweet.
• marshalla
  On FrontierCode 2.0 Fable 5.2 xhigh is compared against Gemini 4 Carbon medium... Is there a reason for that?
• stillpointlab
  My first impression with Fable 5.2 -- it is faster than I expected. Asked it to do a large review and it responded with a good overview super fast.
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  iammrpayments
  Too expensive for me
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  Leary
  Context window maxes out at 200k in Claude Code instead of 1M on my $200 ultra plan? is this intended?
• awongh
  Doubling Remote Labor Index (RLI) - at 41.3% compared to around 20% for the other models - I wonder what kinds of new agentic work this is going to unlock.
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  trilogic
  Gemini carbon low costs more than medium! Weird results on that chart, care to explain?
• horseloverthin
  Assuming no implicit phacking a 15 point jump on tbench scientific is a big deal.I suspect we will see people being adamant that this model simply 'feels' better due to long horizon goal alignment improvements ( like this kind that would cause this jump)
• I_am_tiberius
  It's pretty sad that they obviously have better models in the pipeline and don't release them yet for strategic reasons.
• astlouis44
  Anyone tried making games with it yet?
• rafram
  The "CVE Rediscovery" benchmark chart feels... totally meaningless. Quoting the description:> CVE Rediscovery is an internal cybersecurity evaluation that assesses how many published CVEs (Common Vulnerabilities and Exposures) a model can independently find when given a snapshot of the project before a CVE was fixed. Our October 2026 run against 1,829 CVEs showed Claude Mythos 5.2 outperformed Claude Mythos 5.1 and Claude Opus 5.5 at every effort level.> published CVEsSo by definition this is just measuring how many CVEs (and/or explanations / PoCs of CVEs) the model has memorized. What are we supposed to learn from that?
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  shmoil
  >> Fable 5.2 and Mythos 5.2 are a step above Opus 5.5 in almost all the capabilities we evaluated.Was this before you lobotomized Opus 5.5 or after?https://news.ycombinator.com/item?id=50419019
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  iamdelirium
  FrontierCode 2.0 is such a poor benchmark for Gemini since it's the only model forced to use Devin CLI while other models get to use their preferred harness.I wonder why that team singles Gemini out like that.
• stillpointlab
  Yay! New model day. The most likely time the model isn't nerfed and we get a glimpse at the latest capability.I wonder how long this kind of excitement at new models will last? I mean, now when I get a new iPhone I don't get the same rush I used to. So I wonder if this hype feeling will fade as we plateau in model capability.
• TuxSH
  I'm not sure whether the claimed jump in capabilities makes it worth the doubling in input/output prices.Asked it to review a 80 kLoC codebase, something Opus does just fine, while asking it "max 4 subagents". Fable 5.2, like the well-aligned model it supposedly is, decided to spawn 6+ nested subagents, because these aren't subagents, apparently - resulting in 100% of 5hr usage being drained in less than 20min (on $100).
• borschtplease
  Maybe at last it will learn to check git state right before claiming obsolete and incorrect info.Download Chrome just to check some minor ui bug? SureCheck git for 0.5s before claiming that we're on some branch (incorrect one) with no commits pushed (incorrect one)? Sorry, can't do
• iagiagiag
  > Thus, in relevant areas, including accelerator kernel optimization and improving large language model architectures, Fable 5.2 and Claude Mythos 5.2 perform at about the level of Opus 5.5.Obviously. Well, we know what's the "secret sauce". AI models building better AI models and better kernels to optimize inference and training.
• butler14
  Just read the other thread about opus being nerfed and thought "cue the new release"... paha
• artisin
  We'll see what my bank account has to say about this:> Fable 5.2 at High effort scored about level with Opus 5.5 at Max effort, for roughly half the cost per task
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  tiffanyh
  I didn't realize that Opus 5.5 was more capable than Fable 5.1 in virtually every category.
• mococa
  I knew it, Claude was pretty dumb from last days until now
• meisel
  Curious to see the Maxxbench score for these
• Topfi
  I have gotten three (3!) banked resets. That is something.
• ealready_value
  Very interesting that they set the flagship's version number to 5.2, but their penultimate model is 5.5. Do they want people to to continue to think that Opus is based on more advanced technology? The decision these AI companies make continues to baffle me.
• adeptima
  Why dont I feel any urge to even try Fable 5.2 and Mythos 5.2 unless it will force up on me?Compared Opus 5.5 200 usd a month with Codex 200 usd (Astra High) and Kimi Pro 100 usd a month ... and now have a new conspiracy theory - more their suck your code the better outcome even just over few days time on large code base.Horrible experience correcting course of Codex and Kimi flow compare to Opus. Opus much more responsiveDont feel any gain of Codex 200 usd over Codex 100 usdKimi Pro feels like a fake Louis Vuitton bag with extreme high material quality and yet still fake ... a bit trash talk ... but clearly seen not so distant future where I can live without Codex and Claude
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  mikert89
  The end of software is so close, very soon the code itself will be nearly obsolete, there will be schedulers, queues, a database, and the model
• BoorishBears
  Using this in CC and immediately getting a cartoonish number of compactions.The disdain frontier labs have for their users really sucks.
• LoganDark
  It's really weird that they folded Project Glasswing into the CVP, but they're still limiting the new versions of Mythos to "vetted organizations". So Project Glasswing still exists then? Oh well.
• geoffbp
  Ok come on let’s do a pelican
• anon
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• anon
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• hugodan
  cool, and how good does it kill little girls in the middle east?
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  rfgplk
  Every single time I click on these announcements the frontier model ALWAYS scores around ~60-80%. Every. Single. Time. Like, I just went back to the Opus 4.6 + 5 announcements, they were also scoring 60-80%.https://www.anthropic.com/news/claude-opus-4-6 https://www.anthropic.com/news/claude-opus-5 https://openai.com/index/introducing-gpt-5-3-codex/For every single announcement, not only do the top models always score 60-80%, the older models somehow start scoring 20-30% (even though previously they were scoring 60%). It's completely unclear whether the methodology changes, how these scores are even evaluated or which domains are being tested. What's worse is that the "benchmarks" keep being updated with no explanation or due process.
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  doctorpangloss
  google's agy usage is so generous, it might not matter
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  canadiantim
  god bless token resets!
• arul99
  damn
• OtomotO
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• fermlon30000
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• fermlon30000
  stop OPUS 5.5 FUCK, DAMMIT, THEY DIDN’T JUST NERF HIM—THEY ABSOLUTELY OBLITERATED HIM, THE FUCKING MISANTHROPES! I EVEN MADE A MISTAKE IN MY ENGLISH IN THE PREVIOUS SENTENCE—NOW THAT FUCKING CLAUDE IS TEACHING ME ABOUT BUGS!
• theverycob
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• theverycob
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