StepFun

Step 5 Preview is StepFun's open-weight flagship base model for real-world tasks, with a focus on programming and professional expertise. It is multimodal, taking text, image and video in and text out, with a 1M-token context and adjustable reasoning effort.

Step 3.5 Flash is StepFun's open-weight sparse Mixture-of-Experts model with 196.81B total parameters and about 11B active per token. It uses a 45-layer transformer with 288 routed experts, Top-8 selection, and 256K context for reasoning and agentic tasks.

Step 3.7 Flash is StepFun's open-weight 1T parameter multimodal Mixture-of-Experts model for long-horizon coding, agentic tool use, and image and video understanding. It takes text and image input and supports structured output.