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Claude Fable 5

anthropic.com

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Re: Claude Fable 5

#721

Post by connorboyle »

I gave it a question I've been trying to answer for a long time: "What star designation system does Joseph Needham use in Science & Civilization in China? What star is referred to by the designation '4339 Camelopardi' in that book"?

Fable blew me away with its detailed answer[0] showing a chain of references going from J. E. Bode's 1801 catalogue Allgemeine Beschreibung und Nachweisung der Gestirne to Gustave Schlegel's 1875 work Uranographie Chinoise. I was excited, until I checked scanned copies of the cited books and did not actually find any star with the designation "4339 Camelopardi".

Upon following up with Claude, I was forced to downgrade to Opus, which admitted that Fable's answer was likely a hallucination. Ah, well!

[0]: https://claude.ai/share/0252a3f6-3d29-4de8-a893-010181d8b4e7

Re: Claude Fable 5

#722

Post by 00deadbeef »

Escapade5160 wrote: post #695

It's crazy to release a model that just swaps you to another model when you ask it hard questions. Fable changes to Opus 4.8 when you talk about cybersecurity, biology, and a couple other categories. You still pay Fable input token cost though. Frontier models are stalling, this is anthropic trying to hype the market up. Now they're talking about stopping frontier model research. It's kind of strange how the moment t…

Opus 4.8 already drops to Sonnet when you ask it cybersecurity or biology questions

Re: Claude Fable 5

#723

Post by arthurcolle »

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…

mediocre pelican. very disappointing

Re: Claude Fable 5

#724

Post by Aperocky »

connorboyle wrote: post #721

I gave it a question I've been trying to answer for a long time: "What star designation system does Joseph Needham use in Science & Civilization in China ? What star is referred to by the designation '4339 Camelopardi' in that book"? Fable blew me away with its detailed answer[0] showing a chain of references going from J. E. Bode's 1801 catalogue Allgemeine Beschreibung und Nachweisung der Gestirne to Gustave Schleg…

> I was forced to downgrade to Opus,

So you were forced to downgrade to opus because you dared to challenge the output of fable?

Re: Claude Fable 5

#725

Post by tipiirai »

dannyw wrote: post #255

Impressions from testing Fable 5 prior to launch: • My most noticeable immediate jump was in how its frontend design was much more intentionally crafted, and delightful without feeling like 'AI vibe coded'; with better end-user usability too. • In some internal agentic harnesses, it achieved better results with about half the tokens, making it cost the ~same as Opus 4.8 price-wise! The real price increase is less tha…

Curious about how you tested the frontend design capabilities. Thanks

Re: Claude Fable 5

#726

Post by simonw »

tomjakubowski wrote: post #705
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…

What are some reasons to consider your project instead of Pyodide?

It's difficult to run Pyodide inside server-side Python.

Re: Claude Fable 5

#728

Post by willsmith72 »

It seems way more keen to do stuff without checking with me. So far the results are good, so I'm not complaining, but was definitely a shock.

I usually have 5-10 sessions open so am used to getting some investigations going, coming back 5 minutes later and checking recommendations. This time I just got the fixes. Like I said, so far so good with the results, but it's a mental model shift.

Might need to tune claude.mds if it gets annoying

Also this is going to cause serious whiplash when they remove it from the subscription plan in a couple of weeks. I know I'm not going to suddenly move from $200/m to usage credits

Re: Claude Fable 5

#729

Post by 00deadbeef »

bluelightning2k wrote: post #300

To hide the severity of the price increase, the plan is to move everyone right one model. Haiku = essentially phased out Sonnet = the Haiku use cases Opus = the new Sonnet class Fable = the new Opus class If I am right, the other "5.0" models will be conspicuously absent, possibly even for a couple of months. (If Opus 5 follows soon and is even modestly better than 4.8 then I was wrong.)

I doubt they'll phase out Haiku, some work needs speed more than intelligence. Haiku can answer a lot faster than Sonnet.
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