AnalysisAI ModelsNovember 5, 2026

METR: Anthropic's unreleased Model 4 scores 178.6 on AI capability index

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METR's assessment of Anthropic's unreleased "Model 4," trained September–October 2026, put it at 178.6 on the AI capability index — a jump nearly 90% as large as the entire Opus 4.6 to Mythos 5 improvement. It scored above 50% on all 15 capability benchmarks tested, and the internal-model data pushed METR's estimated acceleration rate to 1.9x versus the 1.7x in Haiku 5.5's system card.

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