For the past few months, Anthropic’s most powerful AI model existed largely as a warning about the dangers of AI. The company refused to release it publicly, repeatedly describing its Mythos-class systems as capable of triggering serious concerns about cybersecurity, biological research (think nasty pathogens) and the accelerating pace of AI development.
The message was clear: this was technology that required extraordinary safeguards before it could be released.
Now Anthropic has done something surprising. It has launched a public version of the same technology, on Claude’s higher-tier subscriptions, albeit for a limited time.
The new Claude Fable 5 is a consumer-facing version of the Mythos-class features that Anthropic previously kept behind closed doors. While the company says it has added extensive guardrails and safety measures, the release marks a significant change from Anthropic. Technology that was once considered too suitable for general availability is now being put into the hands of ordinary Claude users.
Here’s what Fable 5 is good at
According to Anthropic, Fable 5 is built for much more than what you might be using AI for right now, like answering questions or helping you draft an email. The company says it’s designed to handle the kind of work that unfolds over hours, days or even longer, so we’re talking about everything from software engineering projects and in-depth research to complex AI agent workflows.
The big idea is that the Fable 5 can handle a task for a much longer time than previous models. Instead of responding to a single prompt and waiting for the next instruction, it’s meant to be able to work through multi-step problems, keep track of context across long projects, and progress with a greater degree of autonomy.
You can use Fable 5 through the Claude chatbot, but many of its biggest improvements seem to be aimed at power users, researchers, and developers. The goal seems to be to move AI beyond a conversational assistant and closer to something that feels like a true digital collaborator.
Why cyber security is at the heart of the debate
Much of the concern surrounding the Mythos is related to cybersecurity, with Anthropic claiming the model has “the strongest cybersecurity capabilities of any model in the world.” While these properties can help security researchers identify and fix vulnerabilities, they can also be used to discover and exploit the same software vulnerabilities if placed in the wrong hands.
Anthropic acknowledges that “releasing a model like this one carries risks,” and it attempts to address that risk through a unique set of security measures. The model is paired with separate AI systems known as ‘classifiers’ that monitor requests for signs of abuse. When these classifiers detect a request related to advanced cybersecurity activity, the response is handled by Claude Opus 4.8 instead of Fable 5, reducing the risk.
In fact, Anthropic allows public access to Mythos-class features while placing some of the most sensitive areas behind an extra layer of protection. It sounds good – as long as it works.
A positive reception
Initial user reaction has been positive, although users have noted how quickly Fable 5 burns through tokens.
“Fable 5 is insanely good, but watch your usage, I was burning 2% per minute on 20x,” said one Reddit user, who also notes, “I’m on the Max 20x plan and during a heavier session I saw my usage go up about 2% per minute. Not per hour. Per minute.”
Another user takes issue with Fable 5 refusing to deal with cybersecurity, calling it a “preview of AI inequality,” noting that “the public gets the ‘safe’ version. Trusted institutions get the dangerous/beneficial version.”
If you want to use Fable 5, there are a few quirks to its availability that are worth knowing about.
Starting today, Fable 5 is available on Claude Pro, Max, Team and seat-based Enterprise plans at no additional cost. However, Anthropic says that starting June 23, access will temporarily move to a utility credit system.
This means that subscribers who wish to continue using the Fable 5 after this date may need to purchase additional usage credits depending on how much they use the model.
Anthropic says the change is intended to manage demand rather than create a permanent paywall. “After this point – when sufficient capacity allows us to do so – we aim to restore Fable 5 as a standard part of subscription plans,” the company says. “We intend to do this as quickly as we can.”
While early adopters seem happy with the capabilities of Fable 5, its accessibility highlights how advanced AI systems are now, and could point the way to a future where the public no longer has full access to the most advanced models.
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