Anthropic Is Launching a Limited Version of Its Powerful —and Dangerous— Model 'Mythos'

IBL News | New York

Anthropic is putting its most powerful — and dangerous — model in everyone’s hands, but it’s doing it with guardrails and hard safety limits.

On Tuesday, the AI firm launched Claude Fable 5, the first publicly available version of its Mythos model.

Until yesterday, Mythos, Anthropic’s exploit-finding software, was the model the White House wanted kept from China, capped at roughly 200 vetted security organizations.

Fable is Latin for what mythos is in Greek. It’s live for everyone, and it’s the most capable model Anthropic has ever shipped to the public.

Claude Fable 5 is the same as Mythos, except for the safeguards.

In high-risk areas like cybersecurity, biology, chemistry, and distillation, the model blocks responses and falls back to Claude Opus 4.8.

It means that the user asks about cybersecurity, biology, or chemistry, and Claude Opus 4.8 answers instead.

Fable is included on Pro, Max, Team, and Enterprise seats through June 22. On June 23, it comes off those plans and runs on usage credits until capacity catches up.

This Fable, built on Mythos tech, is available for $10 per million input tokens and $50 per million output tokens, double the price of Opus 4.8. That price alone might serve as a deterrent for widespread use. It is available on paid Claude plans until June 22.

A new policy comes with it. Anthropic will keep all Mythos-class traffic for 30 days, including from business customers, to detect jailbreaks. Anthropic says the data won’t be used to train new models.

Fable 5 / Mythos needs less guidance than older models and is already doing incredible things. For example, Stripe pointed Fable at a 50-million-line codebase and got a migration done in a day that would have taken a full team over two months by hand.

Launched as a preview in April, Mythos was initially limited to a handful of partners due to cybersecurity concerns. Last week, Anthropic expanded access to hundreds of organizations across 15 countries, again focusing on organizations that manage critical infrastructure.

Now, a version of that technology is available to anyone through Anthropic’s Claude API and consumption-based Enterprise plans.

Anthropic is also deploying a new version of Mythos, called Mythos 5, to organizations already approved to access the advanced model.

In addition, Anthropic said that it ran an internal bug bounty that has produced no universal jailbreaks over 1,000 hours of testing. “We then worked with external red-teaming orgs, which also failed to find universal jailbreaks,” said the company.

Wary of what a Mythos-class model could do in the wrong hands, Anthropic says it stress-tested its classifiers with jailbreak attempts before releasing Fable 5.

With the launch of Fable 5 and Mythos 5, Anthropic said it will require a 30-day retention on all traffic, even if enterprises previously had zero-retention agreements. The company said it won’t use the data for training and will use it only to “defend against complex and novel attacks, including new jailbreaks,” and “identify and reduce false positives.”

The policy could set an industry precedent in which access to increasingly powerful models comes with mandatory data-retention policies framed as a safety measure.

Vibe-coding platform Base44 said that Fable is better at “one-shotting full apps” and has excellent tool-calling.

Genspark said Fable outperformed every other model in its evaluations and performed significantly better on tasks such as UI design and game coding.

Rakuten said, “What makes highly autonomous operations possible, the extra thinking pays for itself.”

Fable’s launch comes as Anthropic prepares to enter the public markets, alongside OpenAI and Elon Musk’s SpaceX. Anthropic said it expects demand for Fable 5 to be very high.