Claude Fable 5: The first Mythos model is powerful, expensive, and heavily filtered
By Maximilian Schreiner
Building on yesterday's coverage of Fable 5's guardrails, Anthropic released Claude Fable 5, the first Mythos-class model, which leads nearly every benchmark including 95 percent on SWE-bench Verified but costs about twice as much as Opus 4.8. It comes with strict safety filters blocking roughly nine percent of requests and a controversial 30-day data retention policy that overrides zero-data-retention contracts.