AnalysisPolicyOctober 5, 2026

Zvi Mowshowitz reviews model welfare for Mythos 5.1, Fable 5.1 and Opus 5.5

Read original source →thezvi.substack.com

Post combines delayed model-welfare reports for Mythos 5.1 and Fable 5.1 with a new one for Opus 5.5, following earlier entries on Fable and Mythos 5, Opus 5, Opus 4.8 and Opus 4.7. Sections cover an internal Anthropic backroom, perception of the constitution, and early impressions from Antra Tessera and John Wittle.

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