StepFun unveiled Step 5 Preview, a proprietary 600-billion-parameter sparse mixture-of-experts model aimed at long-horizon agent workloads such as software engineering, financial analysis, and professional knowledge work. The model activates roughly 27 billion parameters per token, supports a 1-million-token context window, and accepts both text and image inputs. API access opened at $1.00 per million input tokens and $2.70 per million output tokens, with open weights scheduled to follow on October 15.
