One Hundred Cybersecurity Experts Demand the Ban on Fable 5 Be Lifted

Three days after the U.S. government required Anthropic to disable Fable 5 and Mythos 5, approximately 100 leading cybersecurity experts published an open letter demanding the ban be lifted. According to their assessment, this decision does not make the country safer — it weakens those who protect it and creates a tactical advantage for attackers.

The Case for Defenders

The position of the letter's authors is straightforward. Depriving cybersecurity professionals of the best AI tools at a moment when adversaries continue using them without any restrictions is not a security measure—it is deliberate sabotage of one's own infrastructure. This is precisely how the experts describe the essence of the problem.

"Taking the best AI tools away from defenders while adversaries

continue building them — that is not security, that is sabotage," the open letter states.

Fable 5 and Mythos 5 have already become standard tools in the arsenal of many specialized teams. The models are used for automated malware analysis, real-time vulnerability detection, accelerated incident response, and critical infrastructure monitoring. Their forced shutdown does not make networks safer — it simply redistributes tactical advantage in favor of those who attack.

Who Signed

The letter bears the signatures of approximately 100 experts — researchers from major technology companies, analysts from government agencies, and independent experts. The scope and diversity of signatories reflects a systemic position of the community, rather than narrow professional lobbying. Among their areas of work:

• threat analysis and malware research
• critical infrastructure and industrial control system protection
• zero-day vulnerability and exploit research
• incident response, forensics, and attack investigations
• academic research in AI system security

The authors of the letter are not theorists. They are practitioners who have already integrated Fable 5 into real workflows and have lost access overnight to a tool that became an industry standard for them.

The Logic of the Ban and Its Contradictions

The U.S. authorities' decision was driven by concerns that Fable 5 and Mythos 5 could be used to create cyberweapons or automate attacks.

This is a classic dual-use dilemma: the same capabilities help both defend and attack. The problem is that malicious actors — state-sponsored hackers, organized criminal groups, insiders — are not constrained by American regulatory frameworks. They will easily switch to comparable models from providers in other jurisdictions.

The ban on Anthropic creates an obvious asymmetry: legal defenders lose tools, illegal attackers do not. Moreover, Fable 5 was developed with a focus on safety and alignment, which is precisely what made it attractive to the professional community. If it is responsible AI companies that face regulatory pressure, market incentives will begin working against the goals of regulation itself.

What This Means

The Fable 5 situation exposes a key contradiction in the approach to AI regulation. Security-motivated restrictions often hit precisely those who provide that security. If regulators continue to systematically restrict access to cutting-edge models for legitimate players, the gap between attacker and defender capabilities will only grow. The open letter from one hundred experts is a serious signal to authorities about the real cost of such decisions.