Claude Fable/Mythos 5.1 release and reactions, plus a closer look at cache pricing and benchmark impact - AI News: 9/1/2026, Weekday Roundups (Issue 6.75) (2026-09-02)

https://www.latent.space/p/ainews-claude-fablemythos-51-new

Anthropic released Fable/Mythos 5.1, a Claude-family model release with a context window of 1 million tokens and text plus image modalities. It also cut the prompt cache write price from $1.00 to $0.25 per million tokens. Artificial Analysis Intelligence Index of 66, with 91.4% on FrontierCode. Speculation, attributed to community members, suggests Fable and Mythos may share identical weights with different safety routing.

Source: Latent Space $2026-09-02$.