StepFun Releases Open Weights for Step 5 Preview: 600B MoE, 1M Context

StepFun released the weights of its Step 5 Preview model on October 15, keeping the open-sourcing date it announced at the September launch. The sparse mixture-of-experts model has 600B total parameters with 27B active per token and supports a context window of up to 1 million tokens for long-horizon agent tasks. The weights ship under the StepFun Model License 1.0 with attribution and commercial conditions.

• 600B total parameters, 27B active per token, 1M-token context
• FP8 checkpoint fits on four B300 GPUs or eight H200 GPUs
• 92 layers, Sparse GQA, RL across ~1M verifiable environments
• Released under StepFun Model License 1.0, not a standard open-source license