Claude Fable 5 outpaces GPT-5.5 by 13 points on FrontierMath's toughest problems
Anthropic's new model, Claude Fable 5, posts top scores on the FrontierMath benchmark. According to Epoch AI, Fable 5 hits 87 percent accuracy on tiers 1 through 3 and 88 percent on the hardest tier 4 (v2).
Anthropic's models are getting dramatically better at math in a short span of time. As recently as early 2026, predecessor model Opus 4.5 scored below 10 percent on tier 4. OpenAI's GPT-5.5 reaches about 75 percent on the same tier, well behind Fable 5, although GPT-5.6 is already in the making.
All models were tested on Epoch AI's standard scaffold with maximum reasoning effort. FrontierMath is widely considered one of the toughest benchmarks for AI math reasoning. These math gains aren't just in benchmarks, real-world examples keep stacking up. Most recently, an OpenAI model solved a longstanding Erdős problem; so did Claude Mythos.
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