Claude Fable 5.1 and Claude Mythos 5.1

nezhar

This time it came with a usage reset

scronkfinkle

Has anyone been able to get anything substantial done with Fable in the first place? I more or less had totally given up on using it since the alignment checks were so sensitive that it pretty much always threw me back to Opus.

simonw

Bit of a discount if you're using caching: > same input and output prices, with cache reads at a quarter of the cost This should impact any long-running agent since subsequent calls can benefit from cached reads for previous transcripts.

spicypixel

Yeah but haiku 5 when?

maxdo

Tbh with that price , not even willing to try . What are the benefits for a regular coding agent ? I barely have any errors already with 4.8 level , eg grok 4.6 , gpt 5.6 sol/terra behind router . Why do I need to pay so much money for this ? Any reason ?

re-thc

The biggest change is the price cut of course.

pookieinc

"Price. Fable 5.1 will cost an estimated 25% less than Fable 5 for typical workloads, wherever usage is billed by token. This is because we’re reducing our pricing on cache reads (where the model reads inputs that have already been processed and stored). For highly agentic work, the savings will often be much larger—up to approximately 45%." Glad to see this!

robinpie

do you think we'll go a full year without a new haiku lol

ghoshbishakh

"Content provenance" seems to be activated with this model.

cromka

"with cache reads at a quarter of the cost" OK, I think that's what they meant when they suggested reduced extra promo usage will not sting this much.

eis

I am not sure if Fable is worth it, at least with version 5 vs Opus 5. Opus beats Fable in quite a few benchmarks and at twice the cost I just haven't seen it provide noticeably better results compared to Opus. Has anyone noticed big differences? I did notice Opus maybe making more mistakes repeatedly but I don't have hard numbers on this. I hope Fable 5.1 brings noticeable improvements. I am giving it a go now on my 20x Max plan on a problem that Opus 5 has struggled for more than week now and has made very slow progress with regular regressions on the way.

canadiantim

Thank the heavens for quota resets

niteshpant

I don't know how I feel when all the documentations are written by AI for humans. AI to AI doc share: sure, do what you please. AI to human: please make it legible and flowly. example, "Every thinking block records which model produced it, and it's preserved in one direction only: Claude Fable 5.1 reads earlier models' thinking blocks, and no earlier model reads Claude Fable 5.1's." is a very Claude-isk way of writing. Choppy, long, and lacking flow.

Bluestein

Unless these people start offering free, unlimited inference for a cautionary period so we can test the new model without an up-front (re-)investment, I am not touching this load-bearing pile of neuralese spew with a ten thousand token pole.-

tarr11

“ 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 humans have a token limit too and it can be exhausting to read Claude’s output. Prose density is not the same thing as succinctness.

exabrial

Did we get thought traces back? If no, it's useless.

BoorishBears

At least half the changes are just anti-distillation strategies...

as12fj

"Democratization" through AI means that everyone has to pay a monthly Anthropic tax and only a small secret guild gets access to the real model. Jane Street is a partner? How sad indeed. Anthropic could front run them because they leak all the data.

mlaux

Looks like all three breaking changes are patches for inadvertent chain of thought disclosure. Someone found out (don't have the tweet handy) that if you created a bogus "think_deeply" tool and then forced the model to use it, it would output what is believed to be its raw thinking there - I believe the first breaking change stops this. The second two are aimed at people getting Haiku to repeat thinking blocks from other models verbatim (since it can see the decrypted version). I get that in their eyes it's an "exploit" but still kinda disappointing that they patched this

sashank_1509

Reads like AI slop, surprised they can’t see it in their blog post. No human wants to read in such prose