# Anthropic Releases Claude Fable 5.1 and Mythos 5.1

> Anthropic has shipped two closely related models, Claude Fable 5.1 for general use and a restricted-access Mythos 5.1 aimed at vetted cybersecurity organizations. The pair share the same underlying model but carry different safeguards, a design that lets Anthropic loosen limits for trusted defenders while keeping tighter guardrails for everyone else. The headline numbers are about cost and capability. Fable 5.1 reaches 52.6 percent on Terminal-Bench-Science, more than double the 24.7 percent its predecessor managed, and posts strong results on agentic coding tasks. More consequential for anyone running these models at scale, cache read pricing falls from 1 dollar to 25 cents per million tokens, a 75 percent cut. Anthropic estimates total costs for long-running agent workloads could drop 25 to 45 percent. That combination matters because the expensive part of agentic AI is not a single clever answer, it is the thousands of repeated context reads a working agent racks up. Cheaper caching plus better task performance is exactly the lever that turns demos into affordable production systems.

_Section: [Daily AI Updates](https://www.wortins.com/daily-ai) · Source: VentureBeat · Published Friday, September 4, 2026_

## Wortins' read

Anthropic has shipped two closely related models, Claude Fable 5.1 for general use and a restricted-access Mythos 5.1 aimed at vetted cybersecurity organizations. The pair share the same underlying model but carry different safeguards, a design that lets Anthropic loosen limits for trusted defenders while keeping tighter guardrails for everyone else. The headline numbers are about cost and capability. Fable 5.1 reaches 52.6 percent on Terminal-Bench-Science, more than double the 24.7 percent its predecessor managed, and posts strong results on agentic coding tasks. More consequential for anyone running these models at scale, cache read pricing falls from 1 dollar to 25 cents per million tokens, a 75 percent cut. Anthropic estimates total costs for long-running agent workloads could drop 25 to 45 percent. That combination matters because the expensive part of agentic AI is not a single clever answer, it is the thousands of repeated context reads a working agent racks up. Cheaper caching plus better task performance is exactly the lever that turns demos into affordable production systems.

## Source

[Read the full story at VentureBeat](https://venturebeat.com/technology/anthropics-claude-fable-5-1-and-mythos-5-1-arrive-with-a-75-cost-reduction-for-fable-cache-reads/)

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