Fable 5 redirects cybersecurity, biology, and chemistry queries to Claude Opus 4.8.
Unrestricted Mythos 5 operates solely underneath Undertaking Glasswing with the US authorities.
Anthropic launched on June 9, 2026 Claude Fable 5, the primary mannequin of the Mythos class accessible for normal use. In line with the corporate, the mannequin surpasses in capability all these it has made publicly accessible to this point, with frontier efficiency in software program engineering, scientific analysis and sophisticated data work.
Nevertheless, the agency launched it with mechanisms that block cybersecurity queriesbiology, chemistry and mannequin distillation, redirecting these solutions to Claude Opus 4.8.
The rationale for the blockage refers on to what Anthropic documented within the weeks main as much as the launch. Via Undertaking Glasswing, the restricted program with which Anthropic has distributed Mythos Preview since April, the corporate and its roughly 50 companions discovered greater than 10,000 vulnerabilities of excessive or essential severity in what Anthropic describes as essentially the most systemically vital software program globally.
Analysis members embody Cloudflare, Mozilla, Microsoft, Oracle and Palo Alto Networks, in addition to banks and significant infrastructure establishments.
Cloudflare recognized 2,000 errors in essential path techniques — 400 of them excessive or essential severity.with a false optimistic charge that the corporate group thought-about higher than that of human auditors. Mozilla, for its half, discovered and glued 271 vulnerabilities in Firefox 150, greater than ten occasions what it detected in Firefox 148 with Claude Opus 4.6.
The UK AI Safety Institute famous that Mythos Preview was the primary mannequin to unravel its two end-to-end cyber assault simulations autonomously.
That very same offensive energy is what Anthropic determined to limit in Fable 5. With out safeguards, the mannequin’s capabilities in areas akin to cybersecurity may very well be used improperly to trigger critical injury, the corporate notes in its announcement.
The corporate warns that filters are conservatively calibrated and can typically block innocent requests.
Unrestricted Mythos – Defenders Solely
Fable 5 differs from Mythos 5, its unrestricted counterpart. Mythos 5 has the identical capabilities as Fable 5, however with safeguards lifted in some areas. It would initially be deployed via Undertaking Glasswing, in collaboration with the US authorities, as an replace to Mythos Preview.
Anthropic notes that it has essentially the most superior cybersecurity capabilities of any mannequin on the planet. Though, in comparison with its primary rivals, Anthropic maintains one of the vital restrictive positions in the marketplace. Whereas OpenAI and Google DeepMind have progressively relaxed some filters to extend the usefulness of their fashions, Anthropic continues to prioritize safety, even at the price of limiting performance.
This “constitutional” technique has been each praised by regulators and criticized by builders looking for higher flexibility.
The context by which Fable 5 reaches the general public is that of a documented escalation of assaults in opposition to cryptocurrency infrastructure with AI help. In line with Maximiliano Carjuzaa, co-founder of Cash On Chain, near 100% of the DeFi assaults recorded within the earlier months concerned AI to some extent. Ledger CTO Charles Guillemet warned in April that AI is reducing the barrier to entry for attackers.
In that very same month, the trade recorded a minimum of 34 hacks with losses near USD 635 million, equal to virtually 80% of the whole stolen to this point in 2026.
For the cryptocurrency ecosystem, the arrival of Fable 5 to the general public poses a particular pressure: the identical filters that Anthropic considers enough for normal use haven’t been verified independently within the face of systematic evasion makes an attempt.
Fable 5 blocks cybersecurity queries, however the unrestricted model—Mythos 5—already operates within the fingers of presidency and infrastructure organizations, with capabilities that Undertaking Glasswing logs show as unprecedented in autonomously detecting essential vulnerabilities.
