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

What happened

NVIDIA AI congratulates StepFun on Step 5 Preview, calling it StepFun’s largest open weights release. NVIDIA says the 600B MoE model supports agent tasks lasting up to 24 hours and runs at nearly 8K tokens/sec/GPU on NVIDIA GB300 using NVFP4. StepFun’s quoted announcement lists 27B active parameters per token, a 1M-token context window, native text and vision input, and BF16 and FP8 weights on Hugging Face and ModelScope. NVP4 checkpoint: Deploy with

The story so far

StepFun has released open weights for Step 5 Preview, a 600B mixture-of-experts model, with BF16 and FP8 weights available on Hugging Face and ModelScope, according to its announcement quoted by NVIDIA AI. StepFun lists 27B active parameters per token, a 1M-token context window, and native text and vision input. NVIDIA says the model supports agent tasks lasting up to 24 hours and runs at nearly 8,000 tokens per second per GPU on NVIDIA GB300 using NVFP4.

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