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
Price
Free
Context
256K
Released
Jan 29, 2026
Token volume and request traffic to this model over time.
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.
Yes. The pricing shown on this page for Step 3.5 Flash is zero, so you are not charged for prompt or completion tokens. Free endpoints are rate limited — see the rate limit docs.
Step 3.5 Flash has a 256,000 token context window.
Step 3.7 Flash is another text model from StepFun.
Step 3.5 Flash was released on January 29, 2026.