Anthropic has recorded an impressive milestone as its Claude Fable 5 artificial intelligence model achieved 88% accuracy on the hardest problems in the FrontierMath benchmark. This result outpaces OpenAI's GPT-5.5 by approximately 13 percentage points, representing a significant leap forward in complex reasoning capabilities.
Progress
According to reports from The Decoder, Claude Fable 5's score marks a massive improvement over its predecessor, Opus 4.5, which sat below 10% in early 2026. Meanwhile, OpenAI's latest GPT-5.5 model reached about 75% accuracy on the same ultra-hard tier. This breakthrough indicates that the pace of improvement in AI mathematical problem-solving is accelerating faster than expected.
Context
FrontierMath is known as one of the most rigorous benchmarks today for evaluating the advanced mathematical capabilities of AI. The problems here demand not just mechanical calculation but high-level logical reasoning and abstract thinking. Raising the accuracy rate from under 10% to nearly 90% in a short period suggests that new model architectures have effectively addressed logical computation weaknesses.
Why it matters
For the tech community, these results prove that AI is steadily approaching the capabilities of real mathematicians rather than just serving as basic assistants. While more real-world testing is needed to verify broad applicability, Claude Fable 5's current dominance over OpenAI is reshaping the competitive landscape in the frontier AI model segment.