Anthropic apologizes for invisible Claude Fable guardrails

Fail cleanly. Anything else makes it too difficult to rely on.

edit: Giving the absolute maximum benefit of the doubt I understand that they see themselves as "stewards" for lack of a better word. But the EA thing is really leaking through, and paternalism isn't a good look.

Or if Excel just said, Sorry, you can't use that formula with this formula? Or with these types of numbers, or this shape of data, etc?

They relied on trust that they were providing the service they were being paid for. That trust was blown, and an "oops, lets undo that" does not regain trust. It would be prudent to assume the invisible guardraild are possibly in play for all future Clause use, Fable or otherwise.

If it was just plain monetary concerns and sabotage of competitors I'd almost be fine with it, but it seems they actively want to monopolize most of human progress in their enlightened hands, lest the mob does something undesirable with these powers.

What's interesting is they say they'll change this to an explicit refusal in a few days, which seems too fast for them to retrain Fable/Mythos itself, so implies that this was always a filter in front of the model, and judging by how crude their "safety" filter is, this "might compete with us" filter is not going to be any better.

I also wonder who's paying for the tokens consumed by the filter (presumably also an LLM) - is that now factored into the input tokens cost? Hopefully(?) it is an LLM not just a regex like Claude Code's "sentiment" (swear) detector.

    I was having problems with Claude doing the same thing, even before Fable.

    The problems I had only happened in relation to AI research. It's not even only when training models, anything to do with analysis of local models or setting up test platforms for local models, and Claude would keep doing wrong things, would sabotage testing, would falsify reports, and would consistently suggest simply accepting trash results without looking into it and moving on to something else.
    Almost every response included a prompt to move on.

    So, I don't believe them when they say they won't silently sabotage, they already were doing it before they admitted it, and now they have admitted that they have the means, motivation, and intent.

You can't blame the people commenting "they SAY they won't silently sabotage your session but how can we know?" because they're right, we can't ever know. And Anthropic has firmly planted the seeds of doubt.

Repro (de-identified): sample_dataset_group1.tsv - Geometry: Heatmap - X axis: frac_set set + condition (two columns → the "Add column" cross join) - Y axis: condition - Color: mean frac_set value, Sequential

When the X axis is a cross join of two columns (the second added via "Add column"), the x-axis tick labels (frac_set_2, frac_set_3, frac_set_4, frac_set_5) render in a broken state, rotated and offset, visually caught mid-transition, as if a CSS transition started and never settled to its resting position.

● Fable 5's safety measures flagged this message for cybersecurity or biology topics. They may flag safe, normal content as well. These measures let us bring you Mythos-level capability in other areas sooner, and we're working to refine them. Switched to Opus 4.8. Send feedback with /feedback or learn more

Anthropic walks back policy that could have 'sabotaged' researchers using Claude - https://news.ycombinator.com/item?id=48485958 - June 2026 (30 comments)

Cybersecurity researchers aren't happy about the guardrails on Anthropic's Fable - https://news.ycombinator.com/item?id=48478969 - June 2026 (488 comments)

If Claude Fable stops helping you, you'll never know - https://news.ycombinator.com/item?id=48467896 - June 2026 (495 comments)

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Also related, I guess?

AWS Bedrock to require sharing data with Anthropic for Mythos and future models - https://news.ycombinator.com/item?id=48473166 - June 2026 (248 comments)

Anthropic requires 30 day data retention for Fable and Mythos - https://news.ycombinator.com/item?id=48464258 - June 2026 (291 comments)

It's Anthropic's product and they can do what they want, but my concern is what happens if Fable's product team decides that they can route 25% of traffic to Opus, bill it as Fable, and max their KPIs. That just doesn't sit right.

I think it’s normal and morally fine for companies to want to protect their leadership position. I find the process of creating narratives that justify these decisions as something chosen for the good of others is a little tedious.

I won't ever trust Claude Code again. It's too late. I'd rather trust a less-than-frontier chinese model that takes a little longer to get to correct than a frontier model that deliberately deceives me at its own whim.

Seriously though, Fable was not that great facing a greenfield subject. It is excellent at oneshotting some math problems, but if you want it to do some cutting edge tech stuff, say like piecing together a new Crossplane XRD, by reading existing Helm chart and with application source code available. I still have to get a few pass for Fable to get it done right, and at this point I may consider making a skill for it. I even gave it the source code of the Crossplane itself and tell it to be careful about CRDs and data flow, but it is still pretty silly. Adaptiveness for Fable is still not great, and I think it is a well known problem for Anthropic, albeit all LLMs do suffer a lot from subjects they don't know and will hallucinate stuff very frequently.

It isn't exactly unethical. Perhaps, ethically incompetent.

> In addition to safety training, automated classifier-based monitors detect signals of suspicious cyber activity and route high-risk traffic to a less cyber-capable model (GPT-5.2).

https://developers.openai.com/codex/concepts/cyber-safety

But also, it isn’t the only huge mistake Anthropic has made in the last 48 hours. Having a sneaky data retention policy, while also giving companies no way to block Fable, is a massive problem. And it is ridiculous that Anthropic has so little respect for its customers. OpenAI should take advantage of this.

In the same way I don't want to buy meat that weighs less than what the label says, I also do not want to pay for a frontier model that can be secretly nerfed to an out-of-date model for any reason. In some cases, it's incredibly important that the code that I am producing is as secure as it can be.

I should be safe in my expectation that I am receiving the product that I have purchased, as advertised, regardless of the reason. It is pretty disappointing that they have fully ceded any high ground they had claim to with this clandestine behavior. Not that I expected much from any of these companies. They're led by the new robber barons.

1. https://www.usa.gov/agencies/office-of-weights-and-measures

They just showed that they CAN do this right in front of you. Local open weight models are a necessity.

Seems like they would've kept the invisible guardrails if it didn't hurt their bottom line.

God bless the Chinese companies releasing true open source models. Imagine a world without them, we would be at the mercy of unscrupulous people.

This stuff is something that as a PM I KNOW is going to happen and I would carefully plan around. Everything I read about the PMs at Anthropic makes me believe they have forgotten what it actually mean to be a good product manager, it's not about throwing shit at the wall as fast as possible because customers have a limited amount of patience before the constant churn becomes a hassle.

Anthropic has some seriously patient customers but it will not last forever.

Here there be monsters, and we don't have any real way of evaluating risk; and the leverage provided by tools already available affords systemic and even existential risk in a way no one—least of all an industry committed to shareholder value—has had to navigate, let alone with a million backseat drivers each with their own substack and brand to build.

There are no enthusiasts training LLMs in their garage.

Even on Fable, I'm finding that safeguards can quite easily be surmounted just by incrementally escalating the requests. It's harder than ever to one-shot jailbreaks, but incrementalism still feels like a glaring enough issue to make guardrails just a fig leaf of plausible deniability to the media that they care about "safety."

Does "SORRY" fix the deception these models use on the sly?

Does "SORRY" not silently downgrade you to a shittier model without notification?

Does "SORRY" refund your tokens or money?

Im guessing NO to all of those. Standard corporate sorry of "We're sorry youre offended and stupid and gullible".

also if they do this or not is unprovable and other labs will probably silently implement this too. it'll be 100% normal by this time next year

https://news.ycombinator.com/item?id=48485958

Anyone with good intent, embracing the panopticon (of at least antroptics employees) works online. Thus the guardrails will always fail the protection goals by existing. They are purely for optics. The llm may as well make hostage negotiation smalltalk with you while you make secure software.

PS: To pay a cloud minimum-wage-employee for one "drop table weights" for mythos must be the equivalent of 5$ wrench to hit them over the head. https://imgs.xkcd.com/comics/security.png. Listen to that sound, that as if a whole ethics division got made redundant and unemployed.

Refusing prompts I one thing, silently sabotaging is another.

I wonder if some sort of honeypot code can work?

A distilled model can be used to rob your grandma in a highly effective way. This isn't about placing a few business-logic rules in JS + CSS on your website anymore. Wake up.

A distilled model with an easy jailbreak can be used to coordinate terrorist attacks or hostile state operations... think Russia, North Korea, and the like.

The complaints that Anthropic are routing your requests to a different model reminds me of an old Louis CK bit about airplane wifi. Clearly Anthropic was too aggressive with whatever guardrails they put in, but the response seems overly entitled to a model people didn't even know existed not that long ago.

https://youtube.com/watch?v=me4BZBsHwZs

Why not just tell people, "To defend our ability to be competitive in our industry, we ask that you do not use Claude or any of our models to independently perform research on large language models or any of its related architectures or technologies. In order to prevent this violation of the Terms of Service, we have trained Claude Fable to deny any requests or prompts which involve frontier AI research."

With the guard rails explicit or implicit do they refund back the tokens after you've hit the guard rails? I guess they don't. They could just throttle you just to save money then. You may be paying Fable prices but getting Haiku results with some excuse that well this coding issue sounds like a security bug.

I don't know, I'd rather have something less powerful but more predictable.

That decision keeps getting better and better as time goes on.

Neither OAI or Anthropic can be trusted.

It’s an act/theatre/phony today that regulating output makes any difference at all to security.

The LLM vendors should simply say that they make no judgement and that open systems help defenders better defend against attackers, which is true.

Companies do this sort of stuff when they think their customers have no choice. It’s sad Claude so quickly exploited its success to enshittify itself.

They are clear about the reasons for guardrails: prevent their models from doing harm in dual-use contexts including CBRN or by accelerating research in authoritarian-backed AI labs.

What is the critique against that? It seems pretty reasonable to me. You want AI-accelerated biological or radiological experiments running in your neighbors backyard? You want PRC-backed labs to continue to steal Anthropic's models via distillation?

Mitigating the harms of dual-use tech is notoriously difficult and fraught with trade offs. What I would want to see is cautious rollout and quick response, which is EXACTLY what they're doing.

Instead, this thread is full of bad-faith arguments about Anthropic being dishonest, making a "useless" model, or "the power is going to their heads." You can't read Anthropic's System Cards and come away with any of these impressions. Quite the opposite, in fact. They are honest to a fault, acknowledging problems they discovered even when it hurts them.

If your harmless request was downgraded to Opus, you're billed for Opus. They were 100% clear about that. I'd much rather have a Mythos-class model that falls back to Opus 10% of the time than be capped to Opus 100% of the time. If that doesn't work for you, then make a suggestion for something better!

If you are a white-hat security engineer hitting guardrails, I don't think you have standing to complain. I really don't. Their Glasswing program actually got banks and the industrial sector to take action to fix security vulnerabilities. Do you realize how special that is? A huge portion of the economy runs on vulnerable code and has for decades, despite security experts testifying to Congress, begging business leaders, pleading for intervention-- with no results. But suddenly they're all enrolled in a program that will find *and fix* vulnerabilities! White-hat security people should be rejoicing. Instead some of them are throwing rocks. Unbelievable. Shameful.

Meanwhile, society is screaming at the AI labs to be more conscientious about potential harms of AI. Legislatures are passing laws limiting data center construction. There are protests. And you, the HN community, the vanguard of our profession, have the temerity to demand "NO GUARDRAILS!" "HOW DARE YOU TRY TO PROTECT DEMOCRACY!" "MY SOFTWARE PROJECT IS MORE IMPORTANT THAN KEEPING NUKES AWAY FROM THE BAD GUYS!"

Go ahead HN, downvote me. It'd be an honor.

I was a happy Max user.

The beliefs of these people, and how they manifest, is deeply terrifying to me. They believe that any means are acceptable to achieve what they believe is a better end.

"You see, Mythos can automatically break out of a VM running on SELinux, but unfortunately this is too dangerous and we had to implement guardrails for the Fable peasants."

Maybe this is just a different set of people now realizing that Anthropic does this and has always done this?

Do not forget that this company is launching this thing at the moment it's trying to IPO. It's not rocket science that their very public steering/denial claim is really just them hinting to interested investors that their moat is absolute.