Anthropic releases Fable 5.1 and Mythos 5.1 with major cost cuts
ClaudeOfficial · reddit · 2026-09-02
Anthropic launched Claude Fable 5.1 and Claude Mythos 5.1. Fable 5.1 excels at complex, long-running tasks and research, scoring 52.6% on Terminal-Bench-Science 0.1 (double Fable 5) and 55.8% on Terminal-Bench 4.0 (vs 42.0%). Costs are significantly reduced: lower effort settings match previous high performance, cache reads cost 75% less, reducing costs by 25% for typical workloads and 45% for agentic ones. Safeguards improved, with 60% fewer false positives on cyber requests and 85% fewer fallbacks on biology questions. Fable 5.1 is available everywhere; Mythos 5.1 is via trusted access.
Related event: Anthropic Releases Fable 5.1 and Mythos 5.1 with 75% Cheaper Caching(174 posts)→
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