Anthropic releases Claude Fable 5.1 and Claude Mythos 5.1
Released Claude Fable 5.1 and Claude Mythos 5.1. On company benchmarks, claims 52.6% for Fable 5.1 on agentic scientific research (Terminal-Bench Science 0.1) (Fable 5: 24.7%), 55.8% for Fable 5.1 and 60.9% for Mythos 5.1 on agentic coding (Terminal-Bench 4.0), and 60.9% (no tools) and 65.0% (with tools) on Humanity's Last Exam. Pricing is the same as Fable 5 at $10 per 1M input tokens and $50 for output, but cache reads were cut by 75% to $0.25 per 1M tokens, which it claims lowers costs by about 25% for typical workloads and by up to about 45% for complex coding and highly agentic work. Mythos 5.1 is available only to vetted cyber defenders and life scientists, and is currently limited to US organizations
Why it matters
The competitive axis for frontier models shifts from coding to autonomous scientific research. Tiered deployment that opens the top model only to screened users has hardened into a product line, and the fact that the price cut comes from the cache-read rate rather than from performance shows that long-running agent loops are at the center of billing
Source — Primary sources first; secondary reports are labelled “Press”
Officialanthropic.comhttps://www.anthropic.com/claude-fable-and-mythos-5-1Added in Week 36, 2026 · See that week