As AI models become more powerful, so will the threat level. Anthropic declared the Mythos as too dangerous a model to release to the public some time ago, but its new version, Claude Fable 5, is now available and apparently “safe for general use”.
In a post todayAnthropic explains that Claude Fable 5 is a publicly available “Mythos-class” model that surpasses the capabilities of any other generic AI model Anthropic has ever published.
The capabilities of the Fable 5 exceed those of any model we’ve ever had. It is state-of-the-art in almost all AI benchmarks tested, with exceptional performance in software engineering, knowledge work, vision, scientific research, and many other areas. The longer and more complex the task, the Fable 5 is bigger than our other models.
With Mythos, the fear as a model was mainly around cyber security found quickly find and use exploits in the digital world. With Fable, Anthropic says that there are security measures in place and if a thread comes up that Fable is not allowed to connect to, Closing the case 4.8 will enter the conversation instead. Anthropic says it’s tuned it “conservatively,” so it might kick in more often than you’d expect.
Meanwhile, the Claude Mythos 5 will be available to “a small group of cyber defenders and infrastructure providers” as the same model as the Fable 5, but “with security measures lifted in some areas.”
Mythos 5 will first be deployed via Glasswing projectAs an upgrade to the Claude Mythos Preview, in collaboration with the US government. It has the strongest cyber security capabilities of any model in the world. Soon, we intend to expand access to Mythos 5 through a broader secure access program.
Anthropic adds that “the capabilities of models like Fable 5 and Mythos 5 have the potential to benefit the world greatly,” and that Mythos Preview, Opus 4.8, GPT 5.5 and Pro.
The release of Fable 5 is going to be a little tricky.
Starting today, Anthropic says, the Fable 5 is available for all Pro, Max, Team, and seat-based Enterprise plans, but only until June 23. At that point, Fable 5 will switch to a usage credit-based plan, with the hope of restoring standard access “when sufficient capacity allows.”
- From now until June 22nd, Fable 5 is included at no extra cost on Pro, Max, Team and seat-based Enterprise plans.
- On June 23rd, we will remove Fable 5 from these plans. It will then be required to use use loans. If capacity allows, we will expand the embedded window.
- After that point – when sufficient capacity allows us to do so – we aim to reinstate Fable 5 as a standard part of subscription plans. We intend to do this as soon as we can.
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