StepFun Step 5 Preview

Step 5 Preview is StepFun's coming-soon flagship. The listed size is 600B total parameters with about 27B active, a 1M context window, and text-only input. It is a preview checkpoint, so behavior can still change before a final route. It is not callable, and this catalog does not have published benchmark scores for it. Live 1M-context coding work should stay on DeepSeek or Qwen 3.8 Max.