StepFun posts Step 5 Preview weights
The official Hugging Face card documents a 600B mixture-of-experts model, 27B active, with a 1 million token context.
Official source (opens in a new tab)
StepFun's Hugging Face model card for Step 5 Preview documents the open weights. The official stepfun-ai/Step-5-Preview and stepfun-ai/Step-5-Preview-BF16 repositories were both updated on 15 October 2026. The card calls Step 5 Preview a sparse mixture-of-experts model with 600 billion total parameters, 27 billion active, and a context window of up to 1 million tokens. It says the model accepts text, images, and video, outputs text, and is aimed at agentic work, with a stated strength in finance. The card's licence is the StepFun Model License 1.0, described there as Apache-2.0-style with extra attribution and commercial-use conditions. Serving examples use vLLM and SGLang.
Who it's for: teams that can host a very large open-weight agent model, not a chat app you open in a browser.
Fits: Best Agent Builder and Best for Vibe Coding as a model, not a change to the ranked products.