196.81B / ~11B active (MoE)
Apache 2.0
Open foundation checkpoint in the Step 3.5 Flash release pipeline, with companion Base-Midtrain weights released for code, agentic, and long-context workflows; sparse MoE transformer with 45 layers, 256K context window, and 128,896-token vocabulary; routing uses 288 routed experts plus 1 shared expert with Top-8 activation per token; MTP-based generation acceleration and 3:1 sliding-window/full-attention design for efficient long-context inference; StepFun also released the SteptronOss training code and announced SFT data as coming soon.