StepFun releases Step 5 Preview, a 600B-parameter open-weights AI model

NVIDIA describes Step 5 Preview as StepFun’s largest open-weights release and says the 600B-parameter mixture-of-experts model is built for agent tasks lasting up to 24 hours. StepFun’s model card lists 27B active parameters and a context window of up to 1 million tokens. SGLang provides a deployment guide but says support has not shipped in a standard release; users need its preview Docker image.