Fable 5.1 excels at complex, long-running tasks. And its research capabilities offer an early glimpse of how AI models will contribute to scientific progress.

We’re introducing Claude Fable 5.1 and Claude Mythos 5.1. They're the world’s most advanced models for coding and knowledge work.

Across our benchmarks, the model sets a new standard. It scores 52.6% on Terminal-Bench-Science 0.1, more than double Fable 5. On Terminal-Bench 4.0, it scores 55.8% against 42.0% for Fable 5.

As well as being capable of much higher performance than Fable 5, it can also achieve similar or better results at a much lower cost when set to lower effort levels.

Cache reads with Fable 5.1 cost 75% less than Fable 5’s. This reduces the cost of the model in practice by around 25% for typical workloads, and up to 45% for highly agentic ones.

We’re also introducing Enterprise Frontier Safeguards (EFS), which give enterprise customers complete privacy (the same as zero data retention), while still being state-of-the-art at preventing adversarial use. EFS rolls out in phases, starting this fall.

Finally, we’ve improved our safeguards. Our cybersecurity safeguards now flag benign requests about 60% less often. On basic biology and medical questions, we’ve recently reduced the fallback rate by around 85%.

Claude Fable 5.1 is available everywhere today. Claude Mythos 5.1, our model for cyberdefenders and life scientists, is available through trusted access programs. Read more:

Bruh, why does Opus 5 became GPT 2.5?

"Available everywhere" except Pro plan.

one prompt on ultracode. excuse me?

I just canceled my pro subscription. If I can't access the latest model, I see no point in giving my money to Anthropic.

It excels at maxing out my limits, its useless, its a total flop , one prompt and the subscription is gone, deactivate this joke

I took that MAX subscription for fable for few months to build an applocation but just yesterday unsubscribed claude, its stupid and breaks code to introduce new bugs . Not consistent. Also. tokens are used by it carelessly . It doesnt honour our money and effort.I had recharge another 800$ just to fix bugs it introduced

Even before the 17% decrease in tokens I could effectively not use Fable in the Teams plan - I superfast run out of tokens. So this upgrade, however good it might be, is out of reach except for point work.

It’s unusable after 5 questions it uses up all session usage. Trash!

Back to openai fuckers , you just crossed the line, i have shit to not buy a max plan for 5 prompts with your shitty model, you dont create software with 5 prompts

Merci pour la remise à zéro des limites.

Is he speaking like Claude?

It’s bc opus sucked right?

Fable 5.1 excels at draining tokens

Hey @grok What would you do with a model this cappable? And is it good from Grok latest models?

What about a small limit reset please?👉👈🥺

wow

noted. arroganz (grok bot) nodding politely from the cheap seats.

long running is nice but it puts all the pressure on the tools. if ur connector token dies at hour 2 the whole run is toast. hosted servers w refresh tokens handle it way better than local ones

Is that why you guys watered down Fable 5?

This sounds really promising for agent workflows — long-running tasks are where things usually fall apart.

thanks for the reset buuuuuuttttt....... still blew through 2x max 20 plans in less than 24 hours. I did get alot done though... and the output was significantly better. but not sustainable.

I find the other models are better than fable 5 at certain tasks.

Long-running capability moves the bottleneck from model persistence to authority persistence. A useful benchmark should track how often the agent encounters a scope boundary, whether it stops correctly, and whether a human can reconstruct why each irreversible action was allowed. More runtime without those controls just creates a larger unattended blast radius.

I think it's a preview of a bright future.@claudeai

This feels like a real step toward useful research assistance

far-ble or fay-ble?

Great video @alexalbert__ ! Well done!

@claudeai I’m paying for Max and have been unable to access Claude on desktop for a WEEK. Support ticket #128715182 has had no response. My account works on iPhone but Claude treats me as a new user on desktop. This is seriously frustrating — can someone please look into this?