AnalysisAI ModelsNovember 5, 2026

METR assessment reveals unreleased Anthropic Model 4

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METR's independent assessment scored Anthropic's unreleased "Model 4," trained September–October 2026, at 178.6 on its AI capability index — a jump nearly 90% as large as the entire Opus 4.6 to Mythos 5 improvement. The internal models pushed METR's estimated acceleration rate to 1.9x, versus the 1.7x reported in Haiku 5.5's system card.

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