StepFun releases open weights for Step 5 Preview, a 600B agent model

StepFun published the weights of Step 5 Preview on 15 October 2026, in BF16 and FP8, on Hugging Face and ModelScope. It is a mixture-of-experts model, which uses only some of its parameters for each token: 27B of its 600B are active. It takes text and images and handles up to 1M tokens, input and output combined. StepFun built it for long-running agent work such as coding, and says it is particularly strong at finance.

In StepFun’s own tests it beats the open models Kimi K3 and GLM-5.3 on six of eight benchmarks; GLM-5.3 leads on Terminal-Bench v4 and GDPval-AA v2.1.

In FP8 it runs with vLLM or SGLang on a single node of four B300 GPUs. On StepFun’s API, step-5-preview costs $1 per million input tokens, $0.10 per million cached input tokens and $2.70 per million output tokens.

The StepFun Model License 1.0 allows free use, modification and commercial deployment. A product with more than 100 million active users or over $20 million in revenue in a month must display “Powered by StepFun AI”. Device makers that ship the model as a feature, and companies that run a model-as-a-service business with more than $20 million in total revenue over 12 months, need a separate commercial licence.