Claude Fable 5 surpasses GPT-5.5 by 13 percentage points on the hardest FrontierMath problems
Anthropic's Claude Fable 5 hits 88 percent accuracy on the hardest FrontierMath tier, a massive jump from Opus 4.5, which sat below 10 percent in early 2026. OpenAI's GPT-5.5 reaches about 75 percent on the same tier.
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