Anthropic Releases Top-Tier Claude Fable 5 Publicly, Unveils Mythos Variant Alongside

Anthropic on June 9, 2026 made Claude Fable 5, its first "Mythos-class" top-tier model, publicly available. The company simultaneously announced Claude Mythos 5, which is built on the same base model but with safety guardrails removed and is limited to trusted partners via Project Glasswing. Fable 5 is positioned as the broadly available version equipped with safety mechanisms; its API ID is claude-fable-5, while Mythos 5 uses claude-mythos-5. According to the official announcement, both models are described as especially strong in cybersecurity and biology, and their capabilities led to a cautious approach to public release.