StepFun Step 5 Preview Open Weights: 600B MoE for Agentic AI
StepFun published the open weights for Step 5 Preview on October 15, 2026. It’s a 600B-parameter sparse mixture-of-experts model with 27B active parameters per token, a 1M-token context window and vision input.
Step 5 Preview is the Chinese lab’s flagship model for agentic work. StepFun says it reaches frontier-level performance in software engineering and professional knowledge work, and it is especially strong in finance. The model already ran in StepFun’s products and API. With this release, StepFun delivered on its promise to publish the weights on October 15.
The Hugging Face collection includes BF16 and NVFP4 checkpoints. The license is StepFun Model License 1.0, a permissive license with attribution requirements for redistribution. The model card lists output of up to 1M tokens, which suits long-running agents and large codebases.
The launch matters for the open model race. Commentary on X noted that major Chinese labs had been unusually quiet since late August. Step 5 Preview is one of the largest Chinese open-weight releases this quarter.
FAQ
How many parameters does Step 5 Preview have?
600B total, with 27B active per token in a sparse MoE design.
Where can I download Step 5 Preview?
On Hugging Face under stepfun-ai, in BF16 and NVFP4 formats.