alt Hacker NewsClaude Fable 5.2 and Mythos 5.2
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The lack of transparency around model quality/usage limits on closed models makes me want to ditch them.
What I have learned is that any model from Anthropic/OpenAI is at it's absolute best right after release.
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?
The biggest relief is that the price has dropped by 20%. It’s still expensive, but with my $100 plan, Fable’s usage would spike instantly the moment I started using it, so it was always a source of fear. I will still use opus for general coding design, but for major designs.
Wow
Surprising that Opus 5.5 seems very good still
Here's a 20 page SmallDoc presentation on the most interesting aspects, including:
* Fable designed three electronic devices that worked after human assembly
* Fable solved two black-hole problems and Mythos predicted whole protein shells
* Fable controlled robots to unscrew a cap, solve a cube and draw
https://smalldocs.org/p/claude-fable-52-and-mythos-52-releas...
I used Fable 5.1 today. It looks smooth.I look forward to Fable 5.2 to pick up my code loop holes.
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.
https://artificialanalysis.ai/#intelligence-efficiency-tabs this is the chart that matters for most of poor developers and companies. Pareto for a given intelligence index and looks like only openai is across the quadrant with muse at the bottom. They have really cooked efficient models!
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.
With 5.1, there practically seemed to be no difference in ability between opus and fable, but I hope there is a difference this time. When it seems to struggle while working I end up using astra, so I hope it works well.
"Fable 5.2" name is needlessly confusing versioning.
Having Haiku, Sonnet, and Opus on 5.5 while the higher tier sits at 5.2 means devs now have to explain to their teams why moving from 5.5 to 5.2 is an upgrade
On FrontierCode 2.0 Fable 5.2 xhigh is compared against Gemini 4 Carbon medium... Is there a reason for that?
here is my 2shot-es first person qix clone (one of my personal benchmarks) qretty ok - https://claude.ai/artifact/69k6aLK8W4HgkGzbGuvAzD
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.
Context window maxes out at 200k in Claude Code instead of 1M on my $200 ultra plan? is this intended?
concerning that the models are becoming much better at evading monitors by controlling their visible reasoning, even in deliberate sandabagging (its 25% attempts only). We need more faithful and generalizable monitoring methods.
Damn people were right about 5.5 being nerfed in preparation for a version release. This is not at all a good look.
It's an awesome model spec wise, but I pushed the button, and 10 mins later my whole weekly quota is gone.
I will stick with Sonnet 5.5 - 10 x the amount of work done, at 80% of the quality.
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)
Nerf bench tracking model benchmark performance over time: https://www.bridgebench.ai/nerf-bench
Gemini carbon low costs more than medium! Weird results on that chart, care to explain?
Did anyone get three resets? Been a subscriber since Claude 2 and only got 1.
> To help ensure safety and alignment keep step with growing model capabilities, we ran extensive prerelease safety testing on the model that underlies Fable 5.2 and Mythos 5.2.
So, the difference between them is just the harness?
This is the first frontier model release by them that I am not that moved or eager to go use it, will likely stay on Opus 5.5 or other frontier models.
I am curious as to why they launched this one and why now.
Serious question: What is it good for?
It feels Opus 5.5 has already saturated pretty much software engineering. I use it daily and it's hard to say what it can't do for software engineering. It's perfect.
Fable 5.2 might be useful for some use-cases, but will likely get very little usage.
Anthropic needs to figure out a way to create a new industry (like pushing forward bio/robotics) to get usage for those models.
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.
>> 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?
I just saw a video about a webdev showing a motorcycle site, complete with an animated SVG bike.
He remarked it would've taken him a week to do this.
This made me realize how much computers and user interfaces suck. As a quite enthusiastic, but not very artistic kid, I most certainly did draw bikes like that and even more complex stuff, using nothing but pen and paper.
If your trillion dollar industry makes products that are beaten by pen and paper, I guess there's time for self-reflection.
And the funny thing is, it used to be better than this, using Flash and a drawing tablet was way easier than anything in the HTML era (and more importantly, user friendly), but still way worse than just grabbing a pencil in many ways.
User interfaces just suck, chatbots are somewhat better than most, but I feel the industry hasn't really been progressing in any meaningful sense.
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.
Is it going to be like Fable 5.1? Amazing for first 2 weeks and lobotomised mercilessly after?
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 CVEs
So 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?
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).
Isn't interesting how every model at first is incredible and then a few weeks/months later its bad again, and then the new model is incredible again?
Interesting to see that with each new release there are more benchmarks where they report results on Mythos instead of Fable. For example, this time scientific research is reported on Mythos rather than Fable, showing one more domain where everyday joe can never use these models.
Fable 5.2 may finally be so far ahead of my intelligence that it's not useful for day-to-day tasks. I gave it something to do in a personal project of mine, and took my standard flow of "let's talk about this, explain the options, tradeoffs, blah blah blah" and after 5 minutes my vision was blurry and I was doubting if I even knew how my own project worked. Gave it to Opus 5.5, and instantly got back on track.
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.
Cool! I was hoping for Christmas to have an open weight model which would finally be good, with Fable 5.2 available now they just have time to distill and release a new version which will never get nerfed. Hurray for open weights.
Just read the other thread about opus being nerfed and thought "cue the new release"... paha
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
> 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.
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? Sure
Check git for 0.5s before claiming that we're on some branch (incorrect one) with no commits pushed (incorrect one)? Sorry, can't do
I didn't realize that Opus 5.5 was more capable than Fable 5.1 in virtually every category.
Anybody else started getting the "how is claude doing" messages around the time it was nerfed?
Is it only my impression that in recent model releases every vendor is zooming in on hard skills: code, code, some math + physics ? AI is increasingly Jagged ?
We were promised AI can find cure for cancer and in powerpoints most enterprise value comes from Business-AI.
It might as well be that before business-AI can be done we have to cover the basics at superhuman level. All basics, not just entry level jobs like excels, coding jira tickets.
One-shotting a full game (albeit super impressive) looks like overfitting one skill over explaining why we have not much progress in other areas.
I live in an IT bubble and cannot tell if outside IT/math the models are also getting significantly better ?
It's pretty sad that they obviously have better models in the pipeline and don't release them yet for strategic reasons.
ctrl+f pelican
Hopefully this de-nerfs opus 5.5 as well
i've been trying to use sonnet and opus to keep my usage down on the low max plan, but i noticed today that somehow i'm 80% through my weeks usage. so i'm hesistant to even try fable 5.2 yet, but finding the right set point of usage vs model size has been a bit struggle for me, one of my biggest issues has been trying to pull back doing exhaustive testing or other such things that chew through context, and instead have programs that just measure things are working, but i continously seem to run into issues with claude wanting to repeat things for itself in an adhoc manner. i've tried fable directing opus or sonnet subagents, and the reverse. and i found that part of the issue with smaller models trying to direct subagents is that they over specified what they thought the problem was rather than the problem. like they'll have an "idea" about it which is wrong, and then try and feed that into the subagent.