When Fable 5 is used for frontier LLM development, it does not notify the user and instead limits the model’s capabilities through methods such as prompt modification, steering vectors, and PEFT.

Anthropic estimated that this would affect approximately 0.03% of traffic.

Was using Fable 5 to write my world model training code.

Anthropic flagged it as frontier AI research.

The steering vector kicked in and it started implementing JEPA 🤨

this is the biggest wake-up call to protect and nourish open source AI

if you don't build out sovereign and independent models+infra closed labs will patronize you to an insulting degree

Labs starting to pull up the ladders on the ability to diffuse AI was inevitable. Doing it without telling the user is misaligned.

Mfers stole all our data, trained on it, told everyone how noble they are and are now pulling the ladder behind them

the omohundro drives point towards sophon stun locking the adversaries: this is some real end game stuff

Degrading performance on ML research *without telling the user* is shockingly hostile and a terrible look. That could silently damage all sorts of work, including some of my own. Also the type of thing that could raise the eyebrows of antitrust enforcers worldwide.

Interesting tidbit from the Mythos/Fable system card: Anthropic are invisibly nerfing any requests that target frontier LLM development.

Anthropic’s new Fable 5 safeguards are fascinating.

When the model is used for frontier LLM development, it apparently does not simply refuse or warn the user. Instead, it quietly limits its own effectiveness through techniques like prompt modification, steering vectors, and PEFT.

That means Claude may still answer, but become deliberately less useful for building frontier AI systems, pretraining pipelines, distributed training infrastructure, or ML accelerators.

Anthropic says this should affect only around 0.03% of traffic, but the precedent is big: They are being selectively capability-throttled in strategically sensitive domains.

We should really nationalize anthropic at this point cause this is cuuuuuuraaaaaaazy.

Btw this doesn’t just make the model less useful it will nerf your code and tell you it’s not. Like you legitimately cannot use this. And how are we to know whether it touches inference optimization or even harness engineering, if we’re not alerted?

frontier coding abilities, as long as you're only working on react apps

I don't think these are the actions of the good guys, even if they see themselves that way.

The AI Safety psyop is just to monopolize the ability to produce AI

Now Claude will literally sabotage your efforts to create any sort of AI of your own

They are literally seizing the means of AI production

The real reason they held Mythos back wasn't for your safety, it was for their moat.

looool that's the "hey bigcos, we don't want you to catch up, but please keep paying us shitton" clause.

I am sad that I will not get to use Fable to work on PyTorch. I also think that these interventions are 100% consistent with Anthropic's stated beliefs. Additionally, by being first, Anthropic gives cover to other labs to impose similar limits for their frontier models.

Anthropic didn’t just add guardrails to make Mythos safer; they added guardrails to protect their own IP.

*Their own IP*.

They are still as happy as fuck to build their AI on other people’s IP.

The best part of all these Claude 5 Fable safety measures is I bet the jailbreaking community will still get past them, so the people doing open research in good faith don't get access to the best models but bad actors maybe can.