Step 3.5 Flash tops MathArena at 96.11% on 11B active parameters

MathArena, run by ETH Zurich's SRI Lab and INSAIT, grades models on maths competitions, with separate views for final-answer and proof-based contests. StepFun's post said its Step 3.5 Flash had taken first place in the final-answer competitions, with 96.11% overall and 97% on AIME 2026 I, for 40 cents a run. The boast about size refers to active parameters. Step 3.5 Flash is a mixture-of-experts model that, according to its launch post, has 196B parameters in total of which 11B are active, meaning only a fraction of the network does the work for any given token.

The linked page no longer shows that ranking. The same MathArena view now averages four sets, AIME 2026, HMMT February 2026, Apex and Apex Shortlist, and ranks Step 3.5 Flash 19th at 66.83%, with GPT-5.5 at xhigh effort first on 94.27%. Its AIME 2026 column reads 97%, though that column now covers both 2026 AIME papers, 30 problems, rather than only the first paper StepFun cited. The fall in the average comes mostly from the harder Apex set, where it scores 14%.

StepFun's post does not say which competitions its 96.11% overall averaged, and that figure could not be checked against an archived copy of the page. The ranking was a snapshot of a leaderboard that has since added competitions and newer models, and the score on a single competition is the more stable number to compare.