Anthropic releases Claude Fable 5 amid US security concerns

What happened

Anthropic has made Claude Fable 5 available to Pro, Max, Team, and some Enterprise users, following a security review prompted by concerns raised by Amazon's security team. The model is available through July 7 (with some use capped at 50% of typical levels) and will transition to standard licensing afterward. Anthropic is also offering a competing model, Claude Mythos 5, to certain users.

Why it matters

Amazon's security team flagged potential risks in Fable 5 related to how the model handles harmful requests and software vulnerabilities. Anthropic responded by building safeguards—including a technique called 'safety margin' that prevents harmful responses at a wider range of inputs—and submitted the model for evaluation via the HackerOne bug-bounty program. For businesses, this signals that major AI vendors are now subject to formal security audits and can roll back access if risks emerge, which may reshape how they plan model deployments.

What to watch

The safety-margin approach allows Fable 5 to block harmful requests more broadly than standard safeguards while still supporting legitimate use cases; Anthropic states the new safety technique does not sacrifice capability. Users can request to switch to Opus 4.8 if preferred. A separate government initiative (announced June 2) is establishing frameworks for evaluating security risks in critical AI models, suggesting ongoing formal oversight of this kind.