Anthropic Opens Fable 5 to the Public With Safeguards and Keeps Higher‑Power Mythos 5 for Vetted Partners

Overview

• Anthropic has made Fable 5, a Mythos‑class build, broadly available but set its system to forward requests about cybersecurity, biology, chemistry, and model‑extraction to a less‑capable model called Opus 4.8.
• The company simultaneously offered a less‑restricted Mythos 5 only to selected partners through Project Glasswing, a vetted‑user program developed with U.S. government collaboration.
• Anthropic reports extensive safety testing including more than 1,000 hours of red‑teaming and a bug‑bounty program and says testers did not find any universal jailbreak that bypasses the protections.
• The firm cites clear productivity and scientific wins from Mythos — examples include a reported engineering task completed in a day by Stripe that would have taken two months and a Mythos‑generated E. coli protein hypothesis later appearing in published research — but warns some legitimate queries may be blocked by the new filters.
• The rollout signals a step‑by‑step access strategy that pairs commercial aims and planned IPO activity with tighter controls for dual‑use risks and a pledge to expand trusted access over time.