The Model Index
Models/Labs/StepFun
Lab · 4 models · since Jul 2025

StepFun

StepFun has 4 models on The Model Index, from Step 3 (Jul 2025) to Step 5 Preview (18 Sep 2026). Its strongest is Step 5 Preview, with an estimated index score of ~175 (GPT-4 = 100). 3 have open weights.

4models tracked3 open · 1 closed
~175index score of Step 5 Previewestimate · not yet independently tested
18 Sep 2026latest releaseStep 5 Preview
2current versions2 replaced by newer ones

Every modelnewest first

ModelReleasedWeightsIndex scoreInput $/MOutput $/MContext
Step 5 Preview18 Sep 2026Closed
~175
–––
Step 3.7 Flash29 May 2026Open
not scored yet
$0.20$1.15262K
Step 3.5 Flashreplaced2 Feb 2026Open
not scored yet
$0.10$0.30262K
Step 3replaced25 Jul 2025Open
not scored yet
–––

Index score is fitted from independent evaluations and scaled so GPT-4 = 100; a striped bar is an estimate for a model not yet independently tested. Prices are list prices per million tokens.

Release history4 announcements

The Race →
DateReleaseKindSource
18 Sep 2026Step 5 PreviewFlagshipplatform.stepfun.ai ↗
29 May 2026Step 3.7 FlashOpen weightshuggingface.co ↗
2 Feb 2026Step 3.5 FlashOpen weightshuggingface.co ↗
25 Jul 2025Step 3Open weightsno link

Dates come from each lab's own announcement, linked where one exists.