Claude Fable 5 outpaces GPT-5.5 by 13 points on FrontierMath's toughest 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. The pace of improvement in AI math keeps accelerating. The article Claude Fable 5 outpaces GPT-5.5 by 13 points on FrontierMath's toughest problems appeared first on The Decoder .