# TestingCatalog — Anthropic launches Claude Fable 5.1 and Mythos 5.1

- Company: TestingCatalog (testingcatalog.com)
- Announced: 2026-09-01T23:59:59+00:00
- Category: new-model
- Coverage: not counted
- Announcement: yes
- Group: models
- Source: https://www.testingcatalog.com/anthropic-launches-claude-fable-5-1-and-mythos-5-1/
- Record: https://forck.live/items/8896-anthropic-launches-claude-fable-5-1-and-mythos-5-1
- Subject: AI models / agents / unreleased features
- Models affected: Claude Fable 5.1, Claude Mythos 5.1
- Pricing: Cache reads now cost 75% less at $0.25 per million tokens. Other rates remain $10 per million input tokens and $50 per million output tokens.

Anthropic launched Claude Fable 5.1 and Claude Mythos 5.1, the same model with different safeguards for coding, knowledge work, and scientific research. Fable is generally available now, while Mythos is limited to vetted cyber defenders and life scientists. Anthropic also introduced Enterprise Frontier Safeguards and reduced cache read costs.

## Evidence

Verbatim from https://www.testingcatalog.com/anthropic-launches-claude-fable-5-1-and-mythos-5-1/:

> Anthropic has launched Claude Fable 5.1 and Claude Mythos 5.1, the same model with different safeguards for coding, knowledge work, and scientific research.

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Record: https://forck.live/items/8896-anthropic-launches-claude-fable-5-1-and-mythos-5-1
Catalogue: https://forck.live/llms.txt
Current issue: https://forck.live/feed.md