Claude Fable 5.1 and Claude Mythos 5.1

#1

Post by denysvitali » Tue, Sep 01, 2026, 5:53 PM UTC

What's new in Claude Fable 5.1 – https://platform.claude.com/docs/en/models/fable-5-1/whats-n...

System Card: https://www-cdn.anthropic.com/0339e6a7c5c7b87f5c07798616dc32...

Claude Fable 5.1 and Claude Mythos 5.1
anthropic.com

Re: Claude Fable 5.1 and Claude Mythos 5.1

#2

Post by nezhar » Tue, Sep 01, 2026, 6:04 PM UTC

This time it came with a usage reset

Re: Claude Fable 5.1 and Claude Mythos 5.1

#3

Post by scronkfinkle » Tue, Sep 01, 2026, 6:07 PM UTC

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.

Re: Claude Fable 5.1 and Claude Mythos 5.1

#4

Post by simonw » Tue, Sep 01, 2026, 6:07 PM UTC

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.

Re: Claude Fable 5.1 and Claude Mythos 5.1

#5

Post by spicypixel » Tue, Sep 01, 2026, 6:08 PM UTC

Yeah but haiku 5 when?

Re: Claude Fable 5.1 and Claude Mythos 5.1

#6

Post by maxdo » Tue, Sep 01, 2026, 6:08 PM UTC

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: Claude Fable 5.1 and Claude Mythos 5.1

#7

Post by re-thc » Tue, Sep 01, 2026, 6:08 PM UTC

The biggest change is the price cut of course.

Re: Claude Fable 5.1 and Claude Mythos 5.1

#8

Post by vessenes » Tue, Sep 01, 2026, 6:09 PM UTC

scronkfinkle wrote: post #3

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.

Combo of that, laziness and load-bearing language + the penchant for making up weird dense conceptual names pushed me to sol 5.6. They seem to indicate it is a less annoying writer in the announcement so I’m curious to try it out, though.

Ironically one of their demos is speeding up inference - do us normies get to do that with Anthropic tech??

Re: Claude Fable 5.1 and Claude Mythos 5.1

#9

Post by pookieinc » Tue, Sep 01, 2026, 6:09 PM UTC

"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!

Re: Claude Fable 5.1 and Claude Mythos 5.1

#10

Post by UltraSane » Tue, Sep 01, 2026, 6:09 PM UTC

scronkfinkle wrote: post #3

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.

I have used it to write some scripts but it is incredibly expensive.