Anthropic Releases Fable and Mythos 5.1 With Lower Costs and Reduced Content Restrictions
Anthropic released Fable 5.1 and Mythos 5.1 on Sept 1, 2026, pairing performance upgrades with reduced token costs and fewer false-positive safeguard restrictions. Fable 5.1 is available immediately on cloud platforms and via the Anthropic API, while Mythos 5.1 is limited to registered cybersecurity or life-science partners.