Claude Fable 5 outpaces GPT-5.5 by 13 points on FrontierMath's toughest problems

Editor's take

Anthropic's Claude Fable 5 has demonstrably surpassed OpenAI's GPT-5.5 on a challenging mathematics benchmark, achieving 88% accuracy compared to GPT-5.5's 75%.

This performance leap is significant as complex reasoning and mathematical capabilities remain a key differentiator in the LLM race. The substantial improvement from Claude Opus 4.5, which previously struggled below 10% on this tier in early 2026, indicates accelerating progress in AI's ability to handle nuanced, multi-step problem-solving, a critical area for enterprise adoption.

Future developments will hinge on whether this mathematical prowess translates to broader reasoning tasks, and if OpenAI can effectively counter this advancement with their own next-generation models like GPT-6, which is expected later this year. The sustained performance of specialized models like Fable 5 on niche benchmarks will also influence the development trajectory of more general-purpose LLMs.