Claude AI outperforms GPT-5.5 by 13 points in FrontierMath tier-4 tests, showcasing advanced reasoning and problem-solving ca

Editorial illustration for Claude Fable 5 beats GPT‑5.5 by 13 points on FrontierMath tier‑4 tests

Claude Fable 5 beats GPT‑5.5 by 13 points on...

Claude Fable 5 beats GPT‑5.5 by 13 points on FrontierMath tier‑4 tests

By AI Daily Post Edited by Brian Petersen, Editor-in-Chief

June 13, 2026 • 2 min read

Claude Fable 5 has just posted the highest scores yet on FrontierMath, the benchmark many consider the toughest test of AI math reasoning. While the model clocks 87 percent accuracy on tiers 1‑3, it reaches 88 percent on the most demanding tier 4 (v2), outpacing OpenAI’s GPT‑5.5 by roughly 13 points—GPT‑5.5 stalls around 75 percent on the same tier. The gap is stark when you look back: early 2026 saw Anthropic’s predecessor, Opus 4.5, scoring below 10 percent on tier 4. All figures come from Epoch AI’s standard scaffold, run with maximum reasoning effort.

But the numbers aren’t just academic. Recent real‑world tests show comparable strides: an OpenAI model cracked a longstanding Erdős problem, and Claude Mythos did the same. These results suggest that the math capabilities of large language models are improving quickly, even as OpenAI prepares GPT‑5.6. The latest figures raise questions about how fast the field is moving and what practical applications might follow.

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.

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

Why this matters

We see Claude Fable 5 hitting 88 percent accuracy on FrontierMath’s tier‑4 problems, a full 13 points ahead of OpenAI’s GPT‑5.5, which stalls around 75 percent. That gap is striking, especially when Anthropic’s Opus 4.5 was under 10 percent on the same tier earlier this year. For developers, the numbers suggest a model that can handle more demanding quantitative tasks without extensive prompt engineering.

Founders might view the result as a cue to reassess which API to integrate for finance‑ or science‑heavy applications, though cost and latency remain unknown variables. Researchers will note the rapid improvement trajectory—two generations in months moved from single‑digit to high‑80s performance—yet the benchmark is a single, proprietary test; broader generalization is unclear. Moreover, OpenAI is already working on GPT‑5.6, so the competitive edge could be short‑lived.

In short, the data points to a meaningful step forward for Anthropic, but whether this translates into sustained advantage across diverse workloads is still uncertain.