Anthropic's Claude Mythos 5 Returns After US Government Lifts Infrastructure Ban

Two weeks ago, Anthropic's most powerful AI models were pulled from the internet by a government order. Today, the standoff is partially over. Anthropic announced that the US government has authorized the redeployment of Claude Mythos 5 to a set of US organizations that operate and defend critical infrastructure. Fable 5, the general-purpose version of the same model, remains offline pending further negotiations.

One Model, Two Products, One Shutdown

To understand what just happened, you need to know how these models work. On June 9, Anthropic released Claude Fable 5, the most capable model it had ever made, as generally available. It also did something unusual: it shipped one model as two products, split not by capability but by a layer of safety classifiers.

• Fable 5: routes flagged cyber, biology, chemistry, and distillation requests to the weaker Claude Opus 4.8, while keeping everything else at full capability.
• Mythos 5: the same underlying model with the cyber safeguards lifted, locked to a vetted group of cyber defenders and critical infrastructure operators. Anthropic calls it the strongest cybersecurity model in the world.

Both models are priced at $10 per million input tokens and $50 per million output tokens, less than half the price of the earlier Mythos Preview. The reason for the split is not commercial -- it is existential. During testing, Mythos Preview identified and exploited zero-day vulnerabilities in every major operating system and every major web browser. The oldest bug it found was a 27-year-old flaw in OpenBSD. It autonomously wrote a remote code execution exploit against FreeBSD's NFS server from a 17-year-old bug.

The Freeze: A Jailbreak, a Directive, and a Geopolitical Subplot

On June 12, the US government directed Anthropic to suspend access to Claude Fable 5 and Claude Mythos 5 for foreign nationals, whether located inside or outside the United States, including Anthropic's own foreign national employees. In response, Anthropic disabled access to those models for all customers. The practical effect: Anthropic blocked all public access to both models globally, meaning no users around the world could access them -- even paying enterprise customers and Anthropic employees internally. It was a huge blow and reversal following the public release of Fable and Mythos 5 just three days prior.