Anthropic’s powerful Mythos AI reportedly breached ‘almost all’ NSA classified systems within a few hours during red-team test — report sheds more light on the

Anthropic’s powerful Mythos AI reportedly breached ‘almost all’ NSA classified systems within a few hours during red-team test — report sheds more light on the

Access to Fable 5 and Mythos 5 barred for foreign nationals immediately following security evaluation

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“(This tool) broke into almost all of our classified systems, not in weeks, but in hours,” Rudd reportedly told Warner, as cited by The Economist in a June 14th report that initially went under the radar. The quote then went viral about a week later across several social media platforms, generating claims that Anthropic’s model “hacked the NSA.” In response, the original author issued a public statement yesterday, the 21st, clarifying that the narrative was false. The breach occurred during an authorized internal red-team test in which Mythos was paired with other defensive tools under highly specific simulated environmental conditions.

The story sheds light on the June 12 U.S. government directive barring all foreign nationals , including Anthropic's own non-citizen employees, from accessing the Fable 5 and Mythos 5 models, citing national security concerns. Anthropic responded by disabling the models globally, saying it could not practically enforce nationality-based access restrictions without pulling the systems for everyone.

At the time, the government did not provide detailed public evidence for the move, which marked the first time the United States had applied export controls directly to an AI model rather than to the hardware powering it. Anthropic said the letter it received did not specify the underlying concern, and that it had been given only verbal evidence of a “potential narrow, non-universal jailbreak” that could allow Fable 5 to identify software vulnerabilities.

The Rudd quote now appears to supply the missing context. The security evaluation took place on June 11, one day before the ban was issued on the 12th. Anthropic contends that the cited breach was a narrow jailbreak, one that rival models, including OpenAI's GPT-5.5, also exhibit. According to the company, the flagged behavior amounted to asking the model to analyze a codebase and fix identified issues, which revealed a few minor, already known bugs, rather than a genuine autonomous offensive intrusion. The company says it is working to restore access and is preparing a collaborative risk-management framework with the White House.

NSA using Claude Mythos for 'offensive cyber operations,' report claims

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