In June, Anthropic first released Fable 5, its Mythos-class AI model for Claude. Three months later, Anthropic is enhancing Claude with its new Fable 5. 1 model upgrade.
Source: [9to5Mac](https://9to5mac.com/2026/09/01/anthropic-upgrades-claude-with-new-fable-5-1-model-details-here/)