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 U.S. government’s sudden ban on the flagship models

According to a report by The Economist last week, Anthropic’s powerful Mythos AI model was able to break into “almost all” classified systems belonging to the National Security Agency (NSA) — one of the highest-ranking and most powerful intelligence agencies in the U.S. government — within hours during a controlled security evaluation. The claim came from Sen. Mark Warner, vice chair of the Senate Intelligence Committee, who said Gen. Joshua Rudd, the head of the NSA and U.S. Cyber Command, briefed him on the model’s capability.

“(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.

Public reaction on the ClaudeAI subreddit appears to be split into roughly three camps. The majority see the story as an indictment of the government’s cybersecurity, citing its inability to hire the required level of talent and its history of leaks. A second large group is skeptical of the claim, considering it sensationalist or even an Anthropic marketing stunt. This group points to the lack of details on the supposed break-in and questions the NSA chief’s technical expertise. A minority seems to push back against skeptics, arguing that observers underestimate the exponential growth in AI capabilities. They cite cybersecurity experts’ claims that AI has compressed attack timelines from hours to minutes and that even well-maintained open-source projects are seeing large numbers of vulnerabilities surface.

Despite the dispute and the broader restrictions, Anthropic continues to work closely with the NSA under a specialized arrangement within its Project Glasswing program. The Financial Times reported earlier in June that roughly six Anthropic engineers are embedded directly inside the agency as forward-deployed staff, adapting and customizing Mythos for specific operational applications, with sources indicating the work could extend to infiltrating networks operated by countries including China and Iran.