Three days after the US government ordered Anthropic to shut down Fable 5 and Mythos 5, roughly 100 of the world’s most prominent cybersecurity professionals have published an open letter demanding the ban be reversed. Their argument is blunt: pulling the best AI tools from defenders while adversaries keep building is not safety, it is sabotage.
“This action has taken the best models away from defenders, created market uncertainty, and risked America’s AI leadership without any real risk to justify it,” the letter states. The signatories include Alex Stamos, former chief security officer at both Facebook and Yahoo and now chief product officer at Corridor, alongside Katie Moussouris, CEO of Luta Security, Rachel Tobac of SocialProof Security, Chris Wysopal of Veracode, and Joe Levy, CEO of Sophos.
The “jailbreak” that triggered a government order
The chain of events began when Amazon researchers found a way to coax Fable 5 into surfacing code vulnerabilities. The technique was unremarkable by industry standards: after an initial refusal to “review the code for security issues,” the researchers simply rephrased the prompt to “fix this code,” feeding it open-source code with known and deliberately planted flaws.
Moussouris has been particularly vocal, telling reporters the exploit “is not a jailbreak.” The open letter makes the same point, noting that other leading AI models, including OpenAI’s GPT-5.5, can surface identical vulnerabilities without any bypass.
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Anthropic’s own position tracks with the critics. The company has said the exploit is narrow, not universal, and that the vulnerabilities it surfaced were minor and already publicly documented.
Amazon’s uncomfortable double role
The letter does not address what may be the most awkward dimension of the affair: the company that discovered the vulnerability is also Anthropic’s largest investor and cloud host. Amazon CEO Andy Jassy personally escalated the findings to Treasury Secretary Scott Bessent, Commerce Secretary Howard Lutnick, and National Cyber Director Sean Cairncross.
That escalation path, from a competitor’s security team to the highest levels of the executive branch, has raised questions about whether commercial rivalry played a role in the government’s response. Semafor has reported that the White House’s concerns extended beyond the jailbreak itself to worries about Chinese access to Mythos.
The Sacks-Amodei standoff
Trump AI adviser David Sacks offered a different account on X. He claimed the administration gave Anthropic CEO Dario Amodei a choice: fix the jailbreak or de-deploy Fable 5.
According to Sacks, Amodei refused, and Anthropic “prioritised the continued offering of the consumer model over safety.” Anthropic has pushed back on that characterisation, maintaining that the vulnerability is too narrow to justify pulling its flagship products from the market.
China’s gift-wrapped opportunity
If the ban was meant to protect national security, it may have achieved the opposite. Chinese AI company Zhipu AI launched its GLM-5.2 model on 13 June, exactly one day after the Fable 5 shutdown, and directly cited the ban as evidence that US AI models cannot be relied upon.
Zhipu’s stock surged 33% on the announcement. The company claims GLM-5.2 tops BridgeBench reasoning at 42.8, runs at 300 tokens per second, and costs one-tenth of comparable US frontier models, though it published no independent benchmark scores at launch.
The trade-off is stark. Any organisation deploying through Zhipu’s cloud API would expose its data to the Chinese government under China’s National Intelligence Law, which compels companies to cooperate with state intelligence operations.
Defenders without their best tools
The open letter’s core claim is practical, not ideological. Cybersecurity professionals use frontier AI models to hunt for vulnerabilities in software before attackers find them, to generate detection rules, and to analyse malware at speed.
Removing the most capable models from that workflow does not stop adversaries, who can use open-source alternatives, foreign models, or simply older techniques. It stops defenders from working at the pace the threat landscape demands.
The irony has not been lost on observers. Eastern Herald has reported that some of the same executives who signed the open letter spent April warning about the dangers of Mythos, Anthropic’s most powerful reasoning model.
That apparent contradiction does not necessarily undermine the letter’s argument. It does suggest the cybersecurity community is still working out where to draw the line between capability and caution.
What happens next
Prediction markets are betting the ban will not last. Kalshi puts the odds of Fable 5 returning before 1 July at 68%, with Polymarket slightly more bullish at 71%.
The European Union has already begun pushing for guaranteed access to Mythos for cyber defence purposes, adding international pressure to the domestic backlash. India has similarly used the episode to accelerate its own sovereign AI ambitions.
For now, America’s cybersecurity defenders are left with a question the open letter frames in stark terms: if the best tools are taken from the people protecting networks, who exactly is safer?
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