---
title: "Anthropic Releases Claude Fable 5.1 and Claude Mythos 5.1: 52.6% on Terminal-Bench-Science and 75% Cheaper Cache Reads"
type: signal
url: https://frontiernewswire.com/s/anthropic-releases-claude-fable-5-1-and-claude-mythos-5-1-52-6-on-vfc0348df
published: 2026-09-01T20:30:21.000Z
byline: "Source: Mark Tech Post"
---

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

Source: Mark Tech Post · Published 2026-09-01 · Canonical: https://frontiernewswire.com/s/anthropic-releases-claude-fable-5-1-and-claude-mythos-5-1-52-6-on-vfc0348df

Anthropic has released Claude Fable 5.1 and Claude Mythos 5.1, the same model behind two different safeguard layers. Fable 5.1 is generally available on the Claude API, AWS, Google Cloud, and Microsoft Foundry; Mythos 5.1 remains restricted to vetted organizations under Project Glasswing. Fable 5.1 scores 52.6% on Terminal-Bench-Science 0.1 against 24.7% for Fable 5, ships a 1M token context window, and drops cache reads 75% to $0.25 per million tokens while base pricing holds at $10 and $50. Three API changes are breaking, including the removal of forced tool use. The post Anthropic Releases Claude Fable 5.1 and Claude Mythos 5.1: 52.6% on Terminal-Bench-Science and 75% Cheaper Cache Reads appeared first on MarkTechPost .

In this story: [AWS](https://frontiernewswire.com/companies/aws), [Google Cloud](https://frontiernewswire.com/companies/google-cloud), [Claude Fable 5.1](https://frontiernewswire.com/models/claude-fable-5-1), [Fable 5](https://frontiernewswire.com/models/fable-5), [Mythos 5.1](https://frontiernewswire.com/models/mythos-5-1), [Project Glasswing](https://frontiernewswire.com/topics/project-glasswing)

## Sources

- [Read the original at Mark Tech Post](https://www.marktechpost.com/2026/09/01/anthropic-releases-claude-fable-5-1-and-claude-mythos-5-1-52-6-on-terminal-bench-science-and-75-cheaper-cache-reads/)

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