September 20, 2026 — StepFun released Step 5 Preview, a 600B sparse MoE flagship with 27B active parameters per token. Targets agentic software engineering, professional knowledge work, and finance.
Ranks top three among global open-source models on Artificial Analysis Intelligence Index. Single-task cost claimed at 1/8 of Claude Opus 5. Open weights planned October 15, 2026. Supports 1M token context and native text + vision input.