Anthropic Drops Public Claude Fable 5 — Crypto Braces for the Mythos Hangover 🛡️

Anthropic on Tuesday officially launched Claude Mythos 5, a restricted-access AI model the company says has unprecedented cybersecurity capabilities, alongside Claude Fable 5, a public version of the same architecture with additional safeguards. Mythos 5 will initially be available only to approved cybersecurity organizations, critical infrastructure operators, government partners and selected life sciences researchers, while Fable 5 is being released for general use.

The launch follows months of concern over Mythos' ability to identify software vulnerabilities and conduct complex cybersecurity operations after details of the model leaked online in March. Earlier this year, the U.K.'s AI Security Institute reported that a preview version became the first AI model to complete a 32-step corporate network intrusion exercise without human assistance, and in April Mozilla reported that a preview version of Mythos discovered over 271 vulnerabilities in the Firefox browser. Anthropic said its Mythos-class models "have reached a threshold where they present significant risks."

Anthropic said it had restricted access to Mythos through its Project Glasswing program while researchers evaluated the risks, and stated that it would continue expanding access to Mythos "through a broader trusted access program" for cybersecurity work and biomedical research. The company added that "In consultation with the U.S. government, we plan to steadily expand access to Claude Mythos 5, continuing our periodic addition of new partners, as well as pursuing a trusted access program that allows cybersecurity organizations to apply in a more systematic manner," and that users of Mythos Preview can upgrade to Mythos 5. The launch comes as tensions between Anthropic and President Donald Trump's administration appear to be easing after a public dispute over the use of Claude for military operations, and earlier this month press reports said Anthropic had embedded engineers at the National Security Agency to help deploy its Mythos AI model for cybersecurity operations, reportedly targeting China and Iran.

Alongside Mythos 5, Anthropic released Claude Fable 5, a Mythos-class model built on the same core design but designed for public use. "Fable 5's capabilities exceed those of any model we've ever made generally available," Anthropic said, noting that the public version "was made safe for general use" and uses safeguards that reroute some topics, including cybersecurity, to a different model, Claude Opus 4.8. The company also warned that "Releasing a model this capable comes with risks. Without safeguards, Fable 5's capabilities in areas like cybersecurity could be misused to cause serious damage."

The release has nonetheless drawn concern from crypto market participants, with market commentator The Milk Road warning of possible short-term FUD and price chop. Simon Dedic, founder of venture firm Moonrock Capital, posted to X on Tuesday that with Fable 5, the "cost and skill required to find exploitable flaws in smart contracts is about to drop to basically zero." He added that "for DeFi, this should be a massive wake-up call. Unaudited protocols will become sitting ducks. Known exploits will get replayed on forks around the clock. Even small projects will get targeted simply because trying costs next to nothing now," and suggested users revoke wallet approvals, remove value from protocols and move crypto to fresh hardware wallets. Curve Finance co-founder Michael Egorov, however, said the threat was likely overblown, arguing that the software in which Mythos found vulnerabilities had millions of lines of code while smart contracts have only a few thousand, and that "both humans and 'usual' AI perfectly fit that code in context and can reason well about it." Egorov added that "I suspect we might not be having a wave of DeFi code hacks, but we may see a lot of things in OpSec [operational security] getting hacked (looking like multisig keys compromises) and supply chain attacks on frontend dependencies, and those are way less dangerous in true DeFi."

According to Anthropic, its Mythos model uncovered more than 10,000 high or critical-severity vulnerabilities in "systemically important software," and for open-source projects it identified around 6,200 high or critical-severity vulnerabilities in more than 1,000 projects. The release comes as Anthropic has reportedly confidentially filed for an IPO with the U.S. Securities and Exchange Commission at a potential valuation of up to $1 trillion, a path also being taken by rival OpenAI. A Polymarket market showed an 84% chance that the firm would release the AI model on Tuesday, the day the launches were announced.