150 Cybersecurity Leaders Sign Open Letter Opposing Trump Administration's Anthropic Export Controls

This is a developing story. NCT previously covered the Commerce Secretary Lutnick’s formal threat letter, Anthropic’s negotiations with Washington, and the role of Amazon CEO Andy Jassy in raising concerns.

Nearly 150 cybersecurity leaders have signed an open letter calling on the Trump administration to reverse export control restrictions on Anthropic’s Fable 5 and Mythos 5 models, Axios reported on June 16. The letter represents the first organized pushback from the U.S. security establishment against the administration’s AI model restrictions.

Who Organized the Letter

The open letter was organized by Dan Stamos, the security researcher behind the Defense Department’s bug bounty program, according to Axios. Stamos reportedly examined the security concerns originally raised by Amazon and found that the flagged vulnerabilities in Fable 5 and Mythos 5 are not unique to Anthropic’s models.

The signatories argue that restricting access to advanced AI agents for defensive cybersecurity work weakens U.S. cyber resilience at a time when adversaries are accelerating their own AI capabilities.

The Escalation Timeline

The letter arrives days after Commerce Secretary Howard Lutnick sent Anthropic a formal letter threatening criminal and civil penalties if the company grants foreign nationals access to Fable 5 or Mythos 5 without government authorization, as Bloomberg reported. That letter escalated the June 13 export control directive from a verbal order to a documented legal threat.

Anthropic has kept both models offline for all users, including U.S. customers, since June 13 because it cannot verify citizenship at the API level. The company has sent staff to Washington, D.C. for in-person negotiations with administration officials.

What the Security Community Is Saying

The security community’s core argument is practical: defensive cybersecurity teams use advanced AI models to identify vulnerabilities, analyze malware, and respond to incidents. Cutting off access to Fable 5 and Mythos 5 removes tools that defenders rely on, while doing nothing to prevent adversaries from accessing competing models or developing their own.

Stamos’s finding that the flagged vulnerabilities are not unique to Anthropic undercuts the rationale for singling out Fable 5 and Mythos 5 specifically. If similar security issues exist in models from OpenAI, Google, or other providers, the export control directive targets one company for problems that are industry-wide.

The Broader Policy Question

The open letter puts the Trump administration in a difficult position. The original justification for the export controls was national security, specifically the risk that foreign adversaries could exploit advanced AI capabilities. The security community is now arguing that the controls themselves create a national security risk by degrading defensive capabilities.

The dispute also has competitive implications. While Fable 5 and Mythos 5 remain offline, Chinese AI companies have gained market share and Western AI vendors unable to operate at full capability are losing ground in markets where they previously held an advantage.