StepFun Releases Step 5 Preview: 600B Sparse MoE Model for Extended Agent Workflows

StepFun released Step 5 Preview on September 20, 2026, a 600-billion-parameter sparse mixture-of-experts model designed for long-horizon agent tasks, with open weights arriving October 15 across three quantization formats. The model features 27 billion active parameters per token, a 1-million-token context window, and multimodal support for text, images, and video inputs, positioning it for autonomous software engineering, financial analysis, and professional knowledge work spanning up to 24 hours of continuous operation.