Anthropic Ships Claude Fable 5.1: Up to ~45% Cheaper for Agentic Workloads, Plus Restricted Mythos 5.1
thione · x · 2026-09-07
Anthropic introduced Claude Fable 5.1 and restricted-access Claude Mythos 5.1, billed as the most advanced models for coding and knowledge work, with research capabilities offering an early glimpse of AI contributing to science. They are the same model with different safeguards: Fable 5.1 is generally available, while Mythos 5.1 is limited to trusted access programs for cybersecurity and life-sciences work.
- Price: Thanks to cheaper cache reads, Fable 5.1 costs 25% less than Fable 5 on typical workloads, and up to 45% less for highly agentic work.
- Data retention: A new Enterprise Frontier Safeguards (EFS) system stores data entirely in customer-controlled cloud infrastructure—zero data retention with state-of-the-art abuse prevention—rolling out to enterprises in phases this fall; until then, eligible customers get zero data retention on Fable 5.1.
- Safeguards: False positives drop sharply—60% fewer in cybersecurity.
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