StepFun Step 5 Preview: ~600B MoE Long-Horizon Agent; Open Weights Due Oct 15

T2Covered by 1 source · first reported by China: SCMP Tech / TechNode / Pandaily / KrASIA / Sixth Tone at 28 Sept, 04:05 UTC

StepFun launched Step 5 Preview on September 20, 2026: a ~600B sparse MoE (~27B active) with 1M context for long-horizon agents, API live now and BF16 open weights planned for October 15.