StepFun launches Step 5 Preview: ~600B MoE model for long-horizon agents

StepFun released Step 5 Preview on September 20, 2026 as its flagship base model for long-horizon agent work. The sparse MoE architecture has about 600 billion total parameters, roughly 27 billion active per token across 92 layers, and supports a 1M-token context with text and image input. BF16 open weights are promised for October 15, 2026, while API pricing is around $1.00 input / $2.70 output per million tokens.

• ~600B total parameters, ~27B active per token, 92 layers
• 1M-token context with text and image input
• BF16 open weights promised for October 15, 2026
• API pricing around $1.00 input / $2.70 output per million tokens