StepFun Releases Flagship Step 5 Preview, 600B Open-Source Model Ranks Top 3 Globally

Chinese AI company StepFun has launched its flagship model Step 5 Preview, targeting AI coding, software engineering, professional knowledge work, and finance. The model uses a sparse MoE architecture with 600B total parameters and only 27B active parameters, supporting a 1 million token context window with native text and vision input.

On the global Artificial Analysis Intelligence Index, Step 5 Preview scored 44 points, ranking among the top 3 open-source models worldwide. Its cost per task is just one-eighth of Anthropic Claude Opus 5.

StepFun built StepCodeBench for the model, covering 553 independent code repositories and 33 programming languages. In tests, the model autonomously read ESP32 development docs, turned a dev board into a Vibe Coding keyboard, and ran real debugging tasks for over 3 hours.

The model is fully available now, with complete weights set to be open-sourced on October 15.