[UPDATE] Independent eval: Fable 5.1 measured ~20% costlier per task than Fable 5 despite cheaper cache reads
Anthropic pitched Fable 5.1/Mythos 5.1 as up to ~45% cheaper on agentic work via reduced cache-read pricing, but evaluator Artificial Analysis measured actual cost per task at $3.76 vs $3.14 for Fable 5 — ~20% higher — because token consumption rose ~70%, swamping the per-token savings. It is a recurring pattern worth flagging for enterprise AI-budget risk: headline model-release cost claims can diverge sharply from real-world spend. Single-source (evaluator figures via one publisher); treat as color, not confirmed.