Step 3.5 Flash is StepFun's most capable open-source foundation model. Built on a sparse Mixture of Experts (MoE) architecture, it selectively activates only 11B of its 196B parameters per token. It is a reasoning model that is incredibly speed efficient even at long contexts.
Modalities
Input Price
$0.09per 1M
Output Price
$0.30per 1M
Context
262K
Released
Jan 29, 2026