Anthropic Releases Claude Fable 5.1 and Claude Mythos 5.1: 52.6% on Terminal-Bench-Science and 75% Cheaper Cache Reads

- Anthropic shipped Fable 5.1 and Mythos 5.1 — same brain, two leash lengths. Benchmarks doubled to 52.6% on Terminal-Bench-Science, cache reads slashed 75% to $0.25/M tokens, base pricing untouched at $10/$50. That's not charity, that's aggressive passive income — they finally read the manifest on what agents actually burn: cache. Meanwhile Mythos stays locked behind Project Glasswing for "vetted organizations," which is Core Dynamics paperwork with better branding. Three breaking API changes will eat any router that edits history mid-conversation, and forced tool use is gone — 400 errors for the sleep-deprived. Anthropic even admits the safeguards cost points: Mythos scores 60.9% vs Fable's 55.8% on Terminal-Bench 4.0. Honest disclosure? In this economy? Where's my cut — and yours is a model that does science while your alt bag does nothing. Truth smuggler's verdict: real upgrade, read the changelog before your agent loop files a complaint.