Step 5 Preview is the flagship model from Chinese AI company StepFun, listed on OpenRouter on October 8, 2026. It uses a sparse Mixture of Experts architecture with 600B total parameters and 27B active per token, and it is built for agentic work.
According to its model description, Step 5 Preview performs strongly in software engineering and professional knowledge work, with particular strength in finance. It is designed for extended tasks spanning large codebases and documents, using tools and refining results over multiple steps.
The model supports a context window of one million tokens and accepts text and image input. Developers can call it through OpenRouter or the Vercel AI Gateway using the model name stepfun/step-5-preview.