Claude Fable 5.1 and Claude Mythos 5.1 • Hacker News Board

Re: Claude Fable 5.1 and Claude Mythos 5.1

#441

Post by azalemeth » Tue, Sep 01, 2026, 8:12 PM UTC

felixrieseberg wrote: post #69

(I work at Anthropic) Beyond all the benchmarks, I think Fable 5.1 is a big improvement in writing style. It sounds a lot less stereotypically like other Claude models, has (imho) a much more natural style, and responds to my style instructions more reliably. More work to be done (and we will!) but reading better prose makes me so much happier. Another point I expect not to get much attention until it all happens at…

Thank you for commenting here and having the guts to face the nerderati!

I'm a Claude Max user. I've never been able to use Fable as my work in medical physics involves both particle physics, biochemistry and biology from Python bivitticus to clinical medicine. I am not a US citizen and work in Europe.

Will Fable 5.1 work on any of my problems? Fable 5 refuses outright. Is there anyone I can ask for a review or adjustment of the safeguards? It doesn't seem so, but with Opus at least I'm pretty sure I can infer lots of your training data from now precise they are. Fable is basically useless infuriatingly. I'm just finishing a proper clinical trial in ovarian cancer and trying to make a simulation environment related to our technology.

Re: Claude Fable 5.1 and Claude Mythos 5.1

#442

Post by perching_aix » Tue, Sep 01, 2026, 8:12 PM UTC

precision1k wrote: post #87

tarr11 wrote: post #35

“ Claude Fable 5.1's writing is generally a step up from earlier Claude models, with fewer stock phrases and less unexplained jargon. In some cases, though, its prose is denser than Claude Fable 5's: sentences run longer and there are fewer paragraph breaks.” I cancelled my pro max Claude subscription last week; codex is much more succinct. I am curious if this is getting better. I don’t think Anthropic realizes that…

I've developed a habit of adding into my prompts "please keep your response concise and succinct" or "I'm trying to cram, please only provide the minimum level of technical detail necessary to understand this topic" I find it helps immensely but it'd be nice if I didn't have to do that.

you could apply it on lifecycle hook level, probably the most appropriate place for it

Re: Claude Fable 5.1 and Claude Mythos 5.1

#443

Post by aschobel » Tue, Sep 01, 2026, 8:12 PM UTC

EliasWatson wrote: post #308

To be honest, these frontier model releases have become boring for me. Opus 4.8 was already good enough for most of my use cases. I don't have any projects right now that I would use Fable for instead of Opus. So when I see announcements like this I just think "that's cool I guess" and then go back to using weaker/cheaper models. What's far more exciting right now is models like DeepSeek V4 Flash and GLM 5.3 Flash. T…

fable and friends are useful for long-term agentic stuff like orchestrating glm-5.3 flash implementers and verifying them

Re: Claude Fable 5.1 and Claude Mythos 5.1

#444

Post by skohan » Tue, Sep 01, 2026, 8:12 PM UTC

TeMPOraL wrote: post #129

Someone1234 wrote: post #92

Earlier quoted context omitted.

One thing I've noticed and HATE, is that when you increase thinking-effort, that seemingly increases response-length. Meaning that X.High is longer than High, which is longer than Medium, etc. Which is kind of the inverse of how people work; a really smart person can condense difficult ideas into simple[r] terms. Whereas people who struggle speak a lot but say very little. High/X.High do seem to deliver better qualit…

With LLMs, you're still mostly read things "off the tip of the tongue". A better comparison is observing a smart person talking to themselves while working on a tough problem. EDIT: also there's a reason the dial is called "effort", not "smarts".

I don't think smart people generally solve problems by talking through reasoning steps at a mile a minute. They clear their mind and let the solution come.

Of course I don't know if there's really a way for this to be molded in current LLM's (sounds more like diffusion)

Re: Claude Fable 5.1 and Claude Mythos 5.1

#445

Post by epistasis » Tue, Sep 01, 2026, 8:12 PM UTC

juancn wrote: post #421

velcrovan wrote: post #121

Earlier quoted context omitted.

I have a pet theory that the Opus prose style/smell we all have grown weary of is due at least in part to the models writing more for themselves and each other than for humans. They're packing lots of signal into fewer words and they don't care if it sounds cringe because it works better as glue in long-running tasks. I'm also thinking of the 2017 novel "Void Star" where AIs who operate everything have long since lef…

It may be like what happened in ResNets using blank space in the image as working memory (because they didn't have any), so they would use non-important parts as a scratchpad.

There's a great visualization of this at 28:45 in this video (starting at 23:45 may give good context)

https://youtu.be/QgH9sr7G13Q?is=aHe-eSHUkqQPNuJd

I've been trying to bet my models to use a directory of notes to document decisions and experiments, but providing this outlet has not stopped Claude's abuse of long comments and long unintelligible chat turns.

Re: Claude Fable 5.1 and Claude Mythos 5.1

#446

Post by andy55a » Tue, Sep 01, 2026, 8:13 PM UTC

Exoristos wrote: post #252

Am I alone in not prioritizing the quality of prose produced by my coding agent? My foremost and almost only concern is how well it can engineer software.

When you spend 8 hours a day reading it, it has a pretty big impact. At least to me, its style is exhausting. Also very important for software itself. Documentation, tickets, code comments etc

Re: Claude Fable 5.1 and Claude Mythos 5.1

#447

Post by ThouYS » Tue, Sep 01, 2026, 8:13 PM UTC

madrox wrote: post #405

I am finding that I am now less interested in better models than I am in token budgets. My issue with Anthropic models now is that I don't feel like I can rely on them as a daily driver because they'll dry up before my quota resets. I am becoming dependent on AI to make a living, and I need predictable spend on it. If I know I can't use a model regularly all month, my enthusiasm is limited. I urge Anthropic to get be…

GLM 5.3-flash fits the bill

Re: Claude Fable 5.1 and Claude Mythos 5.1

#448

Post by fearmerchant » Tue, Sep 01, 2026, 8:13 PM UTC

MyFirstSass wrote: post #217

velcrovan wrote: post #121

Earlier quoted context omitted.

I have a pet theory that the Opus prose style/smell we all have grown weary of is due at least in part to the models writing more for themselves and each other than for humans. They're packing lots of signal into fewer words and they don't care if it sounds cringe because it works better as glue in long-running tasks. I'm also thinking of the 2017 novel "Void Star" where AIs who operate everything have long since lef…

It's the complete opposite, it's filled with unreadable noise with almost no signal. It's not some sci-fi thing, most plausible explanation is cost saving measures. Economics drive everything. And Opus 5 and to a lesser extent Fable 5 have clearly been quantised, or they serve different models to different users from various factors, like usage patterns, API vs subs and server load. Here's a tragically funny but high…

I've mentioned this before, but it reminds me of Oswald Bates from In Living Color:

https://www.youtube.com/watch?v=71xxvp5R9hE

Re: Claude Fable 5.1 and Claude Mythos 5.1

#449

Post by perching_aix » Tue, Sep 01, 2026, 8:14 PM UTC

skolos wrote: post #246

precision1k wrote: post #87

Earlier quoted context omitted.

I've developed a habit of adding into my prompts "please keep your response concise and succinct" or "I'm trying to cram, please only provide the minimum level of technical detail necessary to understand this topic" I find it helps immensely but it'd be nice if I didn't have to do that.

why so many people add 'please' when asking machine to do something? Was there actually research that when you SCREAM or curse it follows your instructions better? P.S. Although my wife insists that I should stay polite in case AI overlords remember how I treat them ...

Not to go all ying/yang about it, but just to give a parallel: https://en.wikipedia.org/wiki/Loudness_war - you kinda need silence to draw a contrast with what's meant to be loud.

Separately, my boss confided in us that he's super abusive with his agent, wondering if we are too (no, lol). While I try not to read too much into this (which he doesn't make easy), I also can't help but not really notice a whole lot of amazing agentic delivery differences from his side. On the contrary, while the passion may improve his agent's performance, I'm not sure if it doesn't decrease his, upending the entire theatre.

Re: Claude Fable 5.1 and Claude Mythos 5.1

#450

Post by irthomasthomas » Tue, Sep 01, 2026, 8:14 PM UTC

felixrieseberg wrote: post #69

(I work at Anthropic) Beyond all the benchmarks, I think Fable 5.1 is a big improvement in writing style. It sounds a lot less stereotypically like other Claude models, has (imho) a much more natural style, and responds to my style instructions more reliably. More work to be done (and we will!) but reading better prose makes me so much happier. Another point I expect not to get much attention until it all happens at…

A recent paper demonstrated how to retrieve decoded hidden reasoning traces. The authors found cases where Claude had memorized the answer but hid this fact from the visible response.

It's getting harder to trust Anthropic's models. Will Anthropic now stop hiding Claude's CoT from users? Deliver the tokens people paid for, and prove the models aren't plotting against them. After all, if the idea was to stop Chinese labs from catching up, it didn't work.