More than 40 cybersecurity experts led by former Facebook CSO Alex Stamos published a letter on June 15, 2026, urging the Trump administration to reverse government restrictions on access to Anthropic's frontier model Claude Mythos 5. The experts argue the curbs hurt defenders more than attackers.
June 2026 · Open Letter to U.S. Commerce & National Cyber Director
40+ Security Leaders Demand the U.S. "Free Fable"
Led by former Facebook CSO Alex Stamos, more than 40 cyber chiefs urge the Trump administration to reverse export curbs on Anthropic's Mythos/Fable models — arguing the restrictions hurt defenders far more than attackers.
40+
Cybersecurity leaders, CISOs & researchers signing the letter
~10,000
Critical vulnerabilities found early in Project Glasswing
~2×
Fable 5 price vs. the previous public flagship
From "supply-chain risk" to a full access freeze
A gradual regulatory path through 2026
Feb–Mar
Anthropic designated a supply-chain risk after refusing autonomous-weapons & mass-surveillance uses under Pentagon contracts.
Apr 7
Mythos Preview held back from public release; deployed for defense via Project Glasswing (AWS, Apple, Google, Microsoft).
Jun 9
Fable 5 (hardened guardrails) & Mythos 5 (partially unlocked) released — curbs tightened over jailbreak concerns.
Jun 12
A directive halts foreign-national access; Anthropic suspends access for all users — defenders included.
Three models, three access tiers
Who can use what after June 2026
Mythos Preview
April 7, 2026
Glasswing-only · defensive use · top CTF & multi-stage scores (AISI)
Fable 5
~June 9, 2026
Public version · guardrails restrict cyber/bio tasks · ~2× prior price
Mythos 5
~June 9, 2026
Partially unlocked · continues Glasswing-only access
The defenders' case
Glasswing firms report a major boost in vulnerability discovery
Comparable power already exists in GPT-5.5 & China's Kimi 2.7
Chinese open-weight models are catching up within months
The open questions
Fable 5 guardrails called "a laughingstock in the cyber community"
Some agencies reportedly kept using Mythos despite the blacklist
Anthropic: public Mythos release would need stronger safeguards
Frontier cyber capability cuts both ways — how to balance regulation and access is now the central policy fight.
"Stripping defenders of frontier-model capabilities is dangerous and foolish." — open letter to Commerce Sec. Lutnick & National Cyber Director Cairncross.
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