StepFun releases Step 5 Preview open weights
Confirmed
The takeaway
On Oct 15, 2026 (Beijing time) StepFun made the weights of Step 5 Preview public on Hugging Face and ModelScope, as promised at its Sept 20 API launch: a 600B-total / 27B-active sparse MoE with up to 1M tokens of context, in FP8, BF16 and NVFP4 checkpoints.
Status
- Claim
Confirmed
- Our reporting
- High confidence
- Importance
- 3 of 5
- Last verified
- 15 October 2026
Your AI and this story
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None of these four assistants can know about it. The closest, Claude Opus 5.5, stops 107 days before it.
Key facts
- Repos (HF API): stepfun-ai/Step-5-Preview (FP8, 24 weight shards plus MTP and vision files), stepfun-ai/Step-5-Preview-BF16 and stepfun-ai/Step-5-Preview-NVFP4; all public and ungated, last modified about 01:30 UTC on Oct 15, 2026; license tag ‘other’
- Model card: sparse MoE, 600B total / 27B active parameters, context up to 1M tokens, maximum output up to 1M tokens; the spec table lists text and image input, text output (the introduction also mentions video)
- Positioning (model card): ‘StepFun’s flagship model for agentic work’, with ‘particular strength in finance’; benchmark results are shown only as an image; GDPval-AA v2.1 scores are from Artificial Analysis as of Sept 20, 2026
- Serving: vLLM (dedicated docker image vllm/vllm-openai:step-5-preview), SGLang and a standalone Transformers implementation; FP8 fits one node of 4 B300 or 8 H200 GPUs, BF16 needs 8 B300 or 16 H200 GPUs; recommended sampling temperature 1.0, top_p 0.95
- License, StepFun Model License 1.0: perpetual, royalty-free use, modification and redistribution with a patent grant; ‘A model trained to a material extent on outputs of the Model is deemed to reproduce or contain a substantial part of the Model’ (so such models are derivative works under the licence)
- License conditions: a separate commercial licence is needed (i) by hardware makers (phones, vehicles, smart glasses, wearables, robots, smart-home devices) shipping its capabilities and (ii) by model-as-a-service providers with over $20M revenue in 12 months; products above 100M monthly active users or $20M monthly revenue must display ‘Powered by StepFun AI’. Internal use is exempt
- On time: StepFun had promised Oct 15 at launch; on Oct 13–14 the placeholder repo was still private (HTTP 401). API access (step-5-preview, $1.00/$2.70 per 1M tokens) and OpenRouter listing continue
What happened
StepFun kept the date it set at launch. Shortly after midnight UTC on Oct 15 (morning in Beijing) its three Hugging Face repos became public with full weight files: the main FP8 checkpoint, a BF16 version and an NVFP4 version for Blackwell GPUs, plus ModelScope mirrors. The model card repeats the launch specification (600B total / 27B active MoE, 1M context) and gives deployment recipes for vLLM, SGLang and Transformers.
The weights come with a new licence, the StepFun Model License 1.0. It reads like Apache 2.0 for most users but adds three commercial gates: device makers need a separate licence before shipping Step 5 capabilities in phones, cars, glasses, robots or smart-home products; model-as-a-service providers with over $20M of annual revenue need one too; and very large products must show “Powered by StepFun AI”. It also defines any model “trained to a material extent on outputs of the Model” as a derivative work, which brings distillation from Step 5 under the licence’s attribution and commercial terms.
Why it matters
Step 5 Preview is one of the largest openly downloadable agent models from a Chinese lab, a day after Ant’s 560B Ling 3.1 Flash (MIT). The licence’s distillation clause is unusual for open weights and mirrors the industry argument over distillation that Anthropic’s Oct 12 report revived. The device clause matters because StepFun’s own agent phone (StepX Neo) launched the same week.
Benchmarks remain vendor-reported (shown only as an image). Press coverage of the release was not yet available at writing.
Sources
6 sources from 3 sites. Numbers match the chips in the text.
6 sources: 5 primary, 1 press
Primary
- Hugging Face: stepfun-ai/Step-5-Preview (model card)huggingface.co, code
- Hugging Face: stepfun-ai/Step-5-Preview-BF16huggingface.co, code
- Hugging Face: stepfun-ai/Step-5-Preview-NVFP4huggingface.co, code
- StepFun Model License 1.0 (LICENSE.txt)huggingface.co, docs
- StepFun docs: Step 5 Previewplatform.stepfun.ai, docs
Press
- Pandaily: StepFun Step 5 Preview, 600B MoE, open weights Oct 15 (Sept 20)pandaily.com, press
Changes
- Filed (HF API and model card read directly; resolves upcoming item
[StepFun Step 5 Preview open weights promised for Oct 15](/upcoming/receipts/#2026-10-15-step-5-open-weights))