Claude Fable 5 available in Agent Builder

What it is: Anthropic's most powerful publicly-available model ever — a safety-guardrailed version of their secret Mythos-class model. Think: Mythos-class brains, made safe for general use.

Claude Fable 5, Anthropic's newest top-tier model, is now selectable in the Agent Builder model picker. It's tuned for high-effort reasoning and long-horizon agentic work out of the box, so you can point agents at it without additional configuration.

The default model is unchanged — pick Claude Fable 5 from the model dropdown when building or editing an agent to use it.

Cost: $10 / million input tokens, $50 / million output tokens, which is twice the cost of Anthropic's Opus models. So, this model should truly be used only for the most complex of tasks. Stick to the other models for everything else that's more standard or routine.

For more information on Fable 5, refer to Anthropic's announcement article: https://www.anthropic.com/news/claude-fable-5-mythos-5