StepFun Models

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.

Step 3.7 Flash is StepFun's latest high-efficiency multimodal Mixture-of-Experts model. It pairs a 196B-parameter language backbone with a vision encoder for native image and video understanding, activating roughly 11B parameters per token. The model supports a 256K context window and exposes selectable reasoning levels (high/medium/low), letting callers trade off speed, cost, and depth of reasoning.

Designed for coding, agentic workflows, structured outputs, and long-context productivity tasks.

Step 5 Preview is StepFun's next-generation flagship foundation model for real-world tasks, with a focus on coding and professional knowledge work. It natively supports text, image, and video input, offers a 1M-token context window, and is well suited for workflows that require processing large amounts of information, using tools, and driving tasks through to deliverable results.