The author tests Anthropic’s Mythos-class model, Claude 5 Fable, on tasks from epic poems to complex isochrone maps and research calibration software. Fable autonomously delegates work to cheaper agents, executes multi‐hour workflows, and produces sophisticated outputs, but its decision process remains a black box, shifting the user’s role from hands‐on builder to outcome judge.

• Claude 5 Fable autonomously delegated research to dozens of Sonnet agents (and spun up adversarial agents for edge cases like Pitcairn Island and Grise Fjord) to build a polished isochrone map in hours.
• It ran a nine-and-a-half-hour autonomous build of "Concord," a research calibration tool, complete with a 19-page design spec and production-ready code.
• The user's role shrank to prompting and light feedback while the model made hundreds of unseen micro-decisions, turning oversight into outcome judging rather than hands-on building.