StepFun releases Step 5 Preview, a 600B open-weight MoE model

StepFun released Step 5 Preview as open weights, with FP8 and BF16 checkpoints on Hugging Face and ModelScope. It is a sparse Mixture-of-Experts model with 600B total and 27B active parameters per token, and supports up to 1M tokens of context. It is built for long-horizon agentic work.

Why it matters: Alongside Meta's Muse Spark Open, NVIDIA's Nemotron and DeepSeek, it adds to a wave of large open-weight models from Chinese and US labs, even as China weighs export controls on such models. The low active-parameter count makes a 1M-context agentic model cheaper to serve than its size suggests.