StepFun has published open weights for Step 5 Preview on Hugging Face. The model card for stepfun-ai/Step-5-Preview was last updated on 15 October 2026. TSN’s earlier roundup on 9 October covered only API listings on OpenRouter and Vercel; this post is about the weights release.
What the model is
StepFun calls Step 5 Preview its “flagship model for agentic work.” The card describes a sparse mixture-of-experts model with 600 billion total parameters, 27 billion active parameters and up to 1 million tokens of context. Maximum output is also listed as up to 1 million tokens.
The specification table lists inputs as text and image, and output as text. The introduction on the same card also says the model “accepts text, images, and video.”
Example deployments on the card include vLLM with FP8 on one B300 node with 4 GPUs or one H200 node with 8 GPUs, and BF16 on one B300 node with 8 GPUs or two H200 nodes with 16 GPUs.
The licence is not Apache 2.0
The weights are under the StepFun Model License 1.0, not Apache 2.0. The model card says that licence is an “Apache-2.0-Style license, with additional attribution and commercial-license conditions.” Hugging Face records the licence field as “other.”
Under the licence text, if in any calendar month a commercial product using the model has more than 100 million active users or generates revenue exceeding US$20 million, the product must thereafter prominently display “Powered by StepFun AI.” A separate commercial licence with StepFun is required for hardware device makers who ship the model’s capabilities as a product feature, and for Model-as-a-Service businesses whose group revenue exceeds US$20 million over any consecutive twelve-month period.
Benchmarks are StepFun’s
The card shows benchmark charts for coding, agentic work, professional knowledge work and finance. Those results are StepFun’s own, using its recommended settings. GDPval-AA v2.1 scores on the card are based on Artificial Analysis results as of 20 September 2026. TSN has not tested the model.
What this means
- The weights are public; the licence is not plain Apache. Teams can download Step 5 Preview, but large commercial and MaaS uses face extra conditions.
- This follows the API debut. Step 5 Preview was already listed on OpenRouter and Vercel; the open-weight drop is the new event.
- Treat the scoreboard as the company’s. Chart results are StepFun’s; only the GDPval-AA line is tied to Artificial Analysis’s published scores.
Sources
- Hugging Face, stepfun-ai/Step-5-Preview model card (last updated 15 October 2026). https://huggingface.co/stepfun-ai/Step-5-Preview
- StepFun Model License 1.0, LICENSE.txt in the same repository. https://huggingface.co/stepfun-ai/Step-5-Preview/blob/main/LICENSE.txt
- Hugging Face, stepfun-ai/Step-5-Preview-BF16 (BF16 checkpoint referenced on the card). https://huggingface.co/stepfun-ai/Step-5-Preview-BF16
