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Claude Fable 5

anthropic.com

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Re: Claude Fable 5

#531

Post by GuB-42 »

baq wrote: post #48
sigmar wrote: post #22

The system card is 319 pages, at what point do we call it a "book" instead of a "card"? There's a quote from a METR report on page 52: >We ran [Mythos 5] on 38 of our hardest software tasks, including tasks centered around R&D. [Mythos5] generally outperformed an early checkpoint of Claude Mythos Preview in these, including by succeeding on some tasks that had not been solved by any public model we have previously ev…

> we believe [Mythos 5] is likely unable to fully and reliably automate R&D for frontier projects spanning multiple weeks this is good news, right? right...?

It is certainly good news for those who are selling all these tokens.

Re: Claude Fable 5

#532

Post by firemelt »

unshavedyak wrote: post #511

It's funny, i'm getting close to not caring anymore how much better a model is. I want it to be about as good as 4.8, but most importantly to be very good at following directions, style, etc. I really like Claude for that in general, but i've not measured in months so i'm not a good judge there. I don't think i'll want to "hand off" code for several years, and so reviewing and iterating is becoming my #1 interest. A…

you use workflows/ultracode?

Re: Claude Fable 5

#533

Post by chrisoosthuizen »

bkjlblh wrote: post #220

> In light of the ability of recent models to accelerate their own development, we’ve implemented new interventions that limit Claude’s effectiveness for requests targeting frontier LLM development (for example, on building pretraining pipelines, distributed training infrastructure, or ML accelerator design). Using Claude to develop competing models already violates our Terms of Service, but enforcing this restrictio…

This feels like the start of a much bigger plan for anthropic to close off the use cases of its models and eat any of its competitors.

Re: Claude Fable 5

#534

Post by simonw »

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 WASM to create a sandboxed code execution library: https://github.com/simonw/micropython-wasm

I just told Claude.ai (not even Claude Code - this was the standard Claude chat interface) running Fable 5:

  Clone simonw/micropython-wasm from GitHub
  and research how this could use a full
  Python as opposed to MicroPython
A few prompts later (and I uploaded the zip files from https://github.com/brettcannon/cpython-wasi-build/releases/t... because Claude chat can't access those files itself) and I have a wheel file that bundles Python itself, compiled to WASM:

  uv run --with https://static.simonwillison.net/static/cors-allow/2026/cpython_wasm-0.1.0-py3-none-any.whl \
    cpython-wasm -c 'print(45 ** 56)'
Here's the transcript: https://claude.ai/share/a73b8b8b-8ebc-4fef-9e5c-7438e5e7ae35

(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.)

Re: Claude Fable 5

#536

Post by rastrojero2000 »

bkjlblh wrote: post #220

> In light of the ability of recent models to accelerate their own development, we’ve implemented new interventions that limit Claude’s effectiveness for requests targeting frontier LLM development (for example, on building pretraining pipelines, distributed training infrastructure, or ML accelerator design). Using Claude to develop competing models already violates our Terms of Service, but enforcing this restrictio…

So that's a possible reason why my specific Claude Opus instance seemed to be impossibly stupid and always degenerates into doing really dumb things to my code!

Cool, good to know I can trust Anthropic.

Re: Claude Fable 5

#537

Post by arizen »

baq wrote: post #48
sigmar wrote: post #22

The system card is 319 pages, at what point do we call it a "book" instead of a "card"? There's a quote from a METR report on page 52: >We ran [Mythos 5] on 38 of our hardest software tasks, including tasks centered around R&D. [Mythos5] generally outperformed an early checkpoint of Claude Mythos Preview in these, including by succeeding on some tasks that had not been solved by any public model we have previously ev…

> we believe [Mythos 5] is likely unable to fully and reliably automate R&D for frontier projects spanning multiple weeks this is good news, right? right...?

Probably there will always be frontier surface which frontier model of a given generation would not be able to automate.

Re: Claude Fable 5

#538

Post by duxup »

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…

I feel like it takes me months to be confident in any of these things.

Re: Claude Fable 5

#539

Post by johnnyApplePRNG »

bkjlblh wrote: post #220

> In light of the ability of recent models to accelerate their own development, we’ve implemented new interventions that limit Claude’s effectiveness for requests targeting frontier LLM development (for example, on building pretraining pipelines, distributed training infrastructure, or ML accelerator design). Using Claude to develop competing models already violates our Terms of Service, but enforcing this restrictio…

> Instead, the safeguards will limit effectiveness through methods such as prompt modification, steering vectors, or parameter-efficient fine-tuning (PEFT).

Am I to understand that this is essentially their form of social-platform ghosting instead of banning?

So they're not even going to tell you that the question you're asking is against their rules, they're just going to twist up your question and/or the answer somehow such that you waste your time essentially?

It seems like I ran into this EXACT same functionality from Claude many months ago when I was trying to ask it to research on the web and help me setup the ideal llama.cpp config for local llm inference.

Funny how lost it got through that relatively simple install when we had all of the documentation in the world (and a human dev with 20+ years experience guiding it along) to go by... and simultaneously it's debugging and building high level cryptography code in rust in the other terminal tab.

This is infuriating to learn.

Re: Claude Fable 5

#540

Post by consumer451 »

doginasuit wrote: post #517

I'm still happy with Opus 4.6 and not impressed with all the models that have come out since then. They seem to use significantly more resources with similar or worse results. Hopefully Anthropic will continue to support this tier of model and offer it in their subscriptions, but in any case, there are plenty of viable alternatives.

4.6 stan here. Yes, agreed. However, I will try this model out in Claude Code. Some indicators seem positive.

For the LLM use cases in my own products, you can pull 4.6 out of my dead hands! lol

edit: Fable 5 appears to be the real deal in at least some use cases. Damn.

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