The Day the US Government Shut Down the World's Most Powerful AI — Pentesty

Back to BlogResearchJun 13, 2026 · 10 min read<br>The Day the US Government Shut Down the World's Most Powerful AI<br>Published by Pentesty · AI Security · Regulation

What Happened on June 12, 2026<br>Imagine launching the most advanced artificial intelligence model in the world and, three days later, receiving a call from the government telling you to pull the plug on everything. That is exactly what happened to Anthropic on Friday, June 12, 2026.<br>At 5:21 PM ET, the U.S. Department of Commerce sent a letter to Anthropic CEO Dario Amodei ordering the immediate suspension of access to Claude Fable 5 and Mythos 5 for all foreign nationals, whether inside or outside the United States. Since the company had no practical way to verify every user's nationality in real time, Anthropic made the most drastic call available: it disabled both models for everyone, worldwide.<br>What Were Fable 5 and Mythos 5?<br>To understand the weight of this decision, you need to know what these models actually were.<br>Mythos 5 is described as the AI model with the most advanced offensive cybersecurity capabilities ever developed. It was restricted to a small, vetted group of government partners and critical infrastructure defenders precisely because it could turn newly discovered software vulnerabilities into working exploits within hours. Work that previously took a senior penetration tester weeks could be compressed into a fraction of that time.<br>Fable 5 was the public version of that same model, wearing a safety vest. Its responses on cybersecurity and biology topics were filtered by a set of independent classifiers designed to block offensive requests. In practice, Fable 5 was Mythos on a leash: powerful, capable, but supposedly controlled.<br>The Jailbreak That Triggered Everything<br>Within hours of Fable 5's public launch, a researcher known online as Pliny the Liberator posted on social media claiming to have "liberated" the model. The method required no code exploitation, no reverse engineering, no software vulnerabilities — just carefully crafted prompts.<br>The documented techniques included:<br>Unicode and Cyrillic character substitution — confusing pattern-based classifiers by replacing standard characters with visually identical lookalikes.<br>Long-context reference threading — embedding malicious intent across extended conversations rather than in a single prompt, making it harder for classifiers to detect the overall objective.<br>Information decomposition and reassembly — breaking sensitive requests into innocent-looking subtopics and reassembling the output on the attacker's end.<br>Narrative and fictional framing — disguising sensitive requests as educational or creative content, such as studying for a certification exam.<br>The most alarming result: screenshots showing functional stack buffer overflow exploit code , generated under the guise of studying for the OSED (Offensive Security Exploit Developer) exam. This is precisely the kind of capability that has kept Mythos 5 behind locked doors.<br>How the Government Reacted<br>According to reporting from NBC News, the Wall Street Journal, and CNBC, the Commerce Department acted after a third-party company — not a government agency — claimed to have found a jailbreak method that could unlock Mythos 5's capabilities through Fable 5. Commerce Secretary Howard Lutnick personally signed the letter to Dario Amodei, invoking national security authorities.<br>The directive classified Fable 5 and Mythos 5 as technologies subject to export controls — the same legal framework historically applied to cryptographic algorithms, weapons components, and sensitive military technology. Analysts quickly drew comparisons to the Crypto Wars of the 1990s, when the U.S. government fought to restrict the export of encryption algorithms like RSA, a battle it ultimately lost.<br>Anthropic Complied, But Pushed Back Hard<br>Anthropic followed the directive but was unusually direct in publicly disputing it. In a detailed statement, the company argued:<br>"We believe this is a misunderstanding, and we are working to restore access as quickly as possible."<br>Their technical counterarguments were pointed:<br>The alleged jailbreak amounts to nothing more than asking the model to read a codebase and fix software bugs — something other publicly available models already do without any restriction.<br>The government provided only verbal evidence of a potential jailbreak, with no robust technical demonstration.<br>The same capabilities were already present in OpenAI's GPT-5.5 with no jailbreak required at all .<br>Applying this standard uniformly would require taking down every major AI provider's frontier models .<br>Anthropic also noted that its cybersecurity classifiers operate independently from the core model, meaning that bypassing the chatbot's conversation layer does not actually disable the most critical safety protections.<br>What This Means for Security Professionals<br>This incident opens...