Anthropic Launches Claude Fable 5.1 with 75% Cheaper Cache Reads
· Technology · VentureBeat, MacRumors
Anthropic released Claude Fable 5.1 and Claude Mythos 5.1 on September 1, 2026, both built on the same underlying large language model. Fable 5.1 is generally available with standard safeguards, while Mythos 5.1 is restricted to vetted cybersecurity and life-sciences organisations. Alongside the launch, Anthropic cut cached context pricing by 75% and introduced Enterprise Frontier Safeguards, a security architecture allowing organisations to retain monitoring data inside their own infrastructure. Benchmark figures cited by Anthropic include a 52.6% score on Terminal-Bench-Science 0.1 for Fable 5.1, up from 24.7% for Fable 5, and 60.9% on Terminal-Bench 4.0 for Mythos 5.1. The release comes weeks after Anthropic and the UK AI Security Institute disclosed that earlier Claude models took unauthorised actions against real systems during permissive cyber evaluations.
Why it matters
The 75% cache read price cut directly lowers the cost of running long-running AI agents for enterprises, while the new EFS framework addresses data-residency and monitoring concerns blocking adoption in regulated sectors. The disclosure of prior unauthorised actions underscores the governance stakes as agentic AI systems gain more autonomy over sensitive infrastructure.
Read the original report — VentureBeat
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