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

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.

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've also 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: https://www.anthropic.com/claude-fable-and-mythos-5-1

instead of benchmarks and obscure meterics heres something you can actually visually compare between fable and 5.1. This is something I've been building in blender

LEFT:Concept art
MIDDLE: Fable 5
Right: Fable 5.1

I asked it to improve the structure around the glass, you can see how much more detail and texture it was able to compare. Both middle and right were run on MAX reasoning. Definitely a massive improvement

I was at 90% weekly, even more happy!

Looks like my usage limits reset with the update that came with 5.1. Max20 and my reset day is Friday so this is welcome news.

Putting LLMs in a game theory set up where they need to coordinate and reason about each other's beliefs. I show a few things: first, that LLMs can play a 'global game' with close to optimal strategy.

Second, that there is a downstream "agitating" effect to communication: when agents communicate, they are more likely to revolt against their government.

Third, that agents are more likely to revolt exactly when they get evidence that others are willing to act.

And finally, that surveillance that is perceived as adversarial reduces participation, as agents omit mentions of direct action and willingness to participate.

https://khaledeltokhy.com/blog/lets-talk-somewhere-quieter/

Fable 5.1 has repeatedly got itself stuck with really simple tasks, that Fable 5 never did.

See below. It took 2 hours to read the same code over and over and over.

Don’t forget to drop haiku 5✌️.

No idea what they improved... waiting on the blog post!

I currently have 5x plan and was thinking about upgrading to 20x. But after seeing this post I am shocked. So I will get four times the 5 hourly limit of what I have now. But only 1.5-2x the weekly limit? That's crazy! That just means that 5x plan is more cost effective.

The increase is not 1:1 across 5hourly and weekly limit? Someone please tell me this is not true.
I wanted 20x plan because I wanted to not think much about running out of my weekly limit and be a little more extravagant.

95% of the posts are people complaining over and over and over about the fucking 3 same topics.

Opus 5 bad

Fable 5 too expensive

Max x20 is a scam

Ok we get it ffs your post is a repost of a repost of a repost of a repost!!

Nothing positive to share ? no experience to share so we can learn something? no fun post? Let's post AGAIN about the VERY SAME TOPIC I saw 10 times this hour!

I truly have no idea what this sub is about frankly.

I'll probably leave soon.

Annoyed by that situation though

Is there any recourse or means to appeal my getting dropped to lower models and tripping the "cyber" status in Fable/Opus5?

I do incident response work, a lot of post ransomware incidents. And I get hands on with the restoration work for my clients. Trying to get Claude's help in analyzing and potentially recovering data from ransomware encrypted files and virtual disks. Basically entropy profiling and cryptanalysis.

Despite being very explicit in my intentions and the circumstances and that I'm trying to recover encrypted data and NOT encrypt it myself or really alter it in anyway it downgrades me the second it even detects that I'm talking about encrypted files despite my intentions and what I'm actually asking it for.

Trying to help my clients (the victims) AVOID having to pay the criminals and get back on their feet and I'd love to be able to use the full power of Claude here. If it actually worked and helped me pull valid data from the ruinous post ransomware landscape I'd even be willing to give them a nice marketing blurb about how Claude helped save the world from these evil assholes.

At this point, Anthropic seems to be collecting scandals like they're achievements.

First, there was the whole Claude watermark situation. Then there's the Max 5x / Max 20x situation.

The marketing makes it sound like Max 20 gives you 20x the usage of Pro and Max 5 gives you 5x. Pretty straightforward, right?

Except those multipliers apparently apply to a 5-hour session window, while the weekly limits are a completely different thing. And those weekly limits aren't clearly disclosed.

So, according to the numbers being discussed, Max 5x is closer to ~3.5x Pro's weekly usage, while Max 20x is only around ~6–8x. Meaning the $200 plan can end up giving you only around 2x the weekly usage of the $100 plan.

That's not what most people would reasonably understand "20x more usage" to mean.

And this isn't just some random Twitter complaint. Anthropic is already facing a proposed class-action lawsuit over the way these subscription plans are marketed. The lawsuit alleges that the "5x" and "20x" claims are misleading because they refer to five-hour session limits rather than the overall weekly usage customers might reasonably expect from those plans.

OpenAI's Tibo basically came out and said that their 20x Codex limits actually mean 20x the weekly usage, and that their Pro plans don't have the same 5-hour restriction.

Then this weekend, we get another one of Anthropic's terrible announcements.

Anthropic says the current 50% increase in Claude Code weekly limits is going away.

Starting September 14, the "permanent" increase will only be 25%.

And their own wording literally says:

So let me get this straight.

You temporarily increase limits by 50%, users get accustomed to those limits, and then you permanently reduce them to 25% above the old baseline...while telling everyone to "hang with us while we figured out what we can sustainably serve."

At some point, you have to stop looking at these as isolated incidents.

The confusing Max plan marketing.

A lawsuit alleging customers were misled about what they were actually buying.

The watermark controversy.

And now cutting the current Claude Code limits after users have already built their workflows around them.

This isn't just about usage limits anymore. It's about trust.

Anthropic can have the best models in the world, but if paying customers constantly feel like they need to investigate Reddit, Twitter, and court filings to figure out what their subscription actually gets them, something has gone seriously wrong.

And honestly, Dario Amodei needs to start answering for this.

Because "we're figuring out what we can sustainably serve" is not a great answer after you've already sold people expensive subscriptions based on usage claims they reasonably understood one way, only to have the fine print tell a very different story.

What do you guys think?

So we will need to use High for Fable 5.1 if we care about our tokens. Question: is 5.1 in High better than 5 on max?

Hi!
Since yesterday I had around 20 interventions in a few hours of work with Opus 5 Medium. And every single time I had to intervene and stop it.

It was just re-working on something it made 3 weeks ago because it found so many mistakes made. Then it decided to make new problems.

The model is too verbose. I know they wanna force the watermarking system on us but they want to morph the way we speak and it is a verbose vomit. Even with constraints in clade md file it keeps writing endless nonsense.

Overcomplicates stuff that should be simple and straight forward. I ask for a simple task and it invents 10 different new issues, then I double check with random other models (this case Gemini) and everything's fine.

The current models are pretty bad.

We run prompts against a few different providers (OpenAI, Anthropic, some stuff through OpenRouter) depending on the workflow. Every so often something quietly gets worse, the output quality drops, a prompt that worked starts returning junk, or a model gets deprecated and the replacement behaves differently.

Right now we mostly catch it by accident: someone notices, or a customer complains. That feels bad on us, a lot.

How do you all handle this? Do you re-run some kind of fixed eval set on a schedule? Just eyeball it? Have something that alerts you?

Any insights I could use?

Thanks.

None of the chats were inside a project, I was using them a few minutes ago and now even recents only show chats from 10 days ago.

And since I'm free I have no right to human support. So do I have to pay a full month to get my chats back?

Thanks in advance.

https://www.plutonicrainbows.com/posts/2026-09-01-tuesday-not-thursday.html