A US official told AP that Anthropic’s Mythos model identified vulnerabilities in classified government systems within hours during Project Glasswing tests with intelligence agencies. The Trump administration then barred foreign access to Mythos and its limited Fable 5 model under a security directive, prompting cybersecurity experts to warn that restricting these tools could weaken US defenses.

• Anthropic's Mythos model found vulnerabilities across nearly all tested classified US government systems in hours, not weeks, per NSA/Cyber Command head Gen. Joshua Rudd
• The Trump administration barred foreign nationals from accessing Mythos 5 and Fable 5, and Anthropic responded by disabling the models for all customers, not just foreign users
• Over 100 cybersecurity leaders (including Adobe and Nvidia executives) are pushing to reverse the ban, arguing Mythos isn't uniquely capable—other models do similar security auditing—and restricting it could weaken US defenses against rival states

A private online forum obtained Mythos the day Anthropic began limited company testing. According to a source with screenshots and a live demo, the group has kept using the model regularly without permission.

• A private forum obtained access to Anthropic's unreleased Mythos model the same day limited corporate testing began (April 7), using stolen or leaked credentials rather than hacking in.
• The group has been querying Mythos almost daily since then, with a source providing screenshots and a live demo as proof, though their actual use case remains unknown.
• Anthropic hasn't disclosed how many people have unauthorized access or what data may have been exposed, only confirming it's "investigating" while rotating keys and tightening API access internally.
• The incident raises questions about whether it could slow future AI pilots with major partners like Apple and Amazon.