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Claude Fable 5

anthropic.com

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Re: Claude Fable 5

#911

Post by solumunus »

teiferer wrote: post #769
simonw wrote: post #534

I've spent enough time with this now in Claude Code (and Claude.ai and Claude Code for web) to have an opinion on Fable 5: it's a beast. I'm throwing some VERY difficult problems at at - things I've been dragging my heels on for months - and it's crunching through them very happily. One that I'm willing to share (albeit from just a week ago) - I built a Python library last week that bundles MicroPython compiled to WA…

> It's possible Opus or GPT-5.5 could have done this too, I've not tried the exact same sequence. The Fable vibes are good here, though. And that's the thing. These comparisons are all gut feelings. I'm missing objective unbiased measurements to actually have real comparisons between different models, their different generations, or even just the convention that everybody adds "you are an expert software engineer" an…

Just treat it like an employee with infinite energy. You can never really measure the productivity or ability of employees, it’s just pretty obvious when one is better than another. You’re asking them to do things and they’re either coming up with the goods or they aren’t. You can’t really expect much more from agents either but I’m not sure why you need anything more.

Re: Claude Fable 5

#912

Post by dathinab »

I really wonder how legal that is. Or more precisely suspect it is very much illegal.

like think about it it's pretty much a tool which intentionally silently sabotages you if you try to compete with the tool maker

It is like selling a hammer but putting in the TOS that you must not use it to build a hammer factory and if you do the hammer silently will sabotage you...

Or image Microsoft would add a window kernel job which sometimes crashes Steam "to make it less efficient to use windows to "compete with the MS app store".

Re: Claude Fable 5

#913

Post by PeterStuer »

Switched to Fable 5 this morning, and after half a day I already don't want to go back to Opus.

Decided the best way to test this was to throw it a really meaty bone: a bug in lifecycle management of Chrome processes on Windows 10. Within the code-base I had developed workarounds over time with Sonnet and Opus, and while those reliably mitigated the problems, it always felt like a clutch and had some performance overhead as well as isolation requirements I would rather not have to take forward.

In comes Fable. Rather than examining the code base, and test a few fixes, Fable sets up an entire testing laboratory inclusive its own controllable webserver, fully instrumented to observe both Python as well as the whole OS kernel process environment, develops a suit of error reproduction tests, confirms the problem and the circumstances under which they reproduce, deep dives into the sources of project dependencies to look for the root cause(s), identifies these and confirms those hypothesis with further experiments. Looks for potential fixes in the later releases of the project where the bug originates, confirms this is not fixed, explores the documentation of said project to find other usage patters, expands its test suit to investigate these alternatives, confirms by crosschecking the source and running further tests that these alternatives do not fully solve the root problem, does a comparative experimental analysis of 3 different styles for using the project, checks the stated roadmap and developer activity in the commit history, recommends a switch to a different pattern that still requires a few of the process management workarounds (I told it not to patch external component), but that significantly simplifies the code-base ...

This is going to be a good 2 weeks, but what happens after? I can't afford this on a per token basis for my own projects.

P.S. An yes, midway the final implementation stretch I got the "Fable 5's safety measures flagged this message for cybersecurity or biology topics. They may flag safe, normal content as well. These measures let us bring you Mythos-level capability in other areas sooner, and we're working to refine them. Switched to Opus 4.8. Send feedback with /feedback or learn more"

Opus managed to finish the implementation, but they need to work on that false positive rate.

Re: Claude Fable 5

#914

Post by techblueberry »

PeterStuer wrote: post #913

Switched to Fable 5 this morning, and after half a day I already don't want to go back to Opus. Decided the best way to test this was to throw it a really meaty bone: a bug in lifecycle management of Chrome processes on Windows 10. Within the code-base I had developed workarounds over time with Sonnet and Opus, and while those reliably mitigated the problems, it always felt like a clutch and had some performance over…

> This is going to be a good 2 weeks, but what happens after? I can't afford this on a per token basis for my own projects.

It’s interesting these companies have trained us to think that disruptive intelligence should be affordable to laypersons.

What will happen after two weeks is that people and companies with means who can afford it will get it, and folks without means won’t.

Re: Claude Fable 5

#915

Post by desmond1303 »

larodi wrote: post #792
simonw wrote: post #534

I've spent enough time with this now in Claude Code (and Claude.ai and Claude Code for web) to have an opinion on Fable 5: it's a beast. I'm throwing some VERY difficult problems at at - things I've been dragging my heels on for months - and it's crunching through them very happily. One that I'm willing to share (albeit from just a week ago) - I built a Python library last week that bundles MicroPython compiled to WA…

One thing I can tell you is you are either favored by Anthropic, or your version of the CLI does not exhaust limits, or there's some major bug, as two people around me (myself included) claim it took half an hour to hit the ceiling. Which makes it practically unusable, where the same workflow a day ago produced a good 5-6 hours of workload with several agents.

Or use API billing? We have access to it at my company with no limits

Re: Claude Fable 5

#916

Post by pythonaut_16 »

theodorewiles wrote: post #546

Here's a song it wrote for me (suno arranged). Not sure if it's AI psychosis but scary good IMO. https://suno.com/s/98uSGabHN42G3YHc

Within the first second it's recognizable as a Suno song. And not even the best example from Suno. (They rhyme structure and rhythm is weird)

Re: Claude Fable 5

#917

Post by [deleted] »

teiferer wrote: post #769
simonw wrote: post #534

I've spent enough time with this now in Claude Code (and Claude.ai and Claude Code for web) to have an opinion on Fable 5: it's a beast. I'm throwing some VERY difficult problems at at - things I've been dragging my heels on for months - and it's crunching through them very happily. One that I'm willing to share (albeit from just a week ago) - I built a Python library last week that bundles MicroPython compiled to WA…

> It's possible Opus or GPT-5.5 could have done this too, I've not tried the exact same sequence. The Fable vibes are good here, though. And that's the thing. These comparisons are all gut feelings. I'm missing objective unbiased measurements to actually have real comparisons between different models, their different generations, or even just the convention that everybody adds "you are an expert software engineer" an…

[deleted]

Re: Claude Fable 5

#919

Post by XCSme »

simonw wrote: post #46

Pelican for Fable 5 on default settings is a clear improvement on Opus 4.8 Fable 5 default: https://gist.github.com/simonw/036bee5a703e7ec84e34efa974438... Opus 4.8 (the "max" one is closest to Fable): https://simonwillison.net/2026/May/28/claude-opus-4-8/#and-s... Now here are the Fable pelicans for all five of the thinking effort levels - low, medium, high, xhigh, max: https://tools.simonwillison.net/markdown-svg-r…

It also does A LOT better, for my hamster test: https://aibenchy.com/showcase/?q=claude#showcase=6efb87c28e3...

Re: Claude Fable 5

#920

Post by ksimukka »

The safeguards of fable are blocking me on almost every task. I would like to see if fable is improved over opus for reverse engineering related work. Back to opus for me.
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