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FrontierThe Decoder
KeyRank 92Claude Fable 5 outpaces GPT-5.5 by 13 points on FrontierMath's toughest problems
Anthropic has dramatically closed the reasoning gap with OpenAI. Claude Fable 5's jump from <10% to 88% accuracy on frontier math signals a fundamental shift in who owns AI's reasoning tier.
Why it ranks · · Claude Fable 5: 88% accuracy on FrontierMath hardest tier · 2026-06-13
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