Step 5 Preview weights now open · StepFun 600B MoE with 27B active and 1M context
StepFun published open weights for Step 5 Preview on 2026-10-15. BenchGecko lists it at $1 input and $2.70 output per M tokens with a 1,048,576 token context window.
What changed
StepFun published open weights for Step 5 Preview on 2026-10-15, the date it committed to at launch. The model first shipped on 2026-09-20 through StepFun's products and API. BF16 and FP8 checkpoints are on Hugging Face and ModelScope, with an NVFP4 build alongside.
BenchGecko updated the row today: open weights flag set, Hugging Face id added, licence recorded, and the release date corrected from 2026-10-08 to 2026-09-20 to match StepFun's launch post.
Specs
From StepFun's model card, API docs and technical blog:
- Architecture · sparse MoE, 600B total parameters, 27B active per token
- Depth · 92 transformer blocks, Gated Sliding Window Attention interleaved 3:1 with Sparse GQA full attention
- Context · 1M tokens, stored as 1,048,576 on BenchGecko
- Max output · 64K tokens on the StepFun API, 64,000 on BenchGecko
- Inputs · text, images and video on the API
- Output · text
- Reasoning effort · low, medium, high
Licence
Weights ship under the StepFun Model License 1.0. StepFun describes it as an Apache-2.0 style licence with additional attribution and commercial licence conditions, so it is not plain Apache.
Self-hosting
StepFun's reference setups:
- FP8 · one node with 4 B300 GPUs, or one node with 8 H200 GPUs
- BF16 · one node with 8 B300 GPUs, or 2 nodes of H200 GPUs
- Runtimes · vLLM and SGLang with an OpenAI-compatible API, plus a standalone Transformers path for offline generation
Pricing on BenchGecko
BenchGecko lists Step 5 Preview at $1 input, $0.05 cached input and $2.70 output per M tokens. The StepFun and DeepInfra endpoints carry the same price. The StepFun endpoint serves 1,000,000 tokens of context and DeepInfra 1,048,576. Uptime over the last day: StepFun 97.4%, DeepInfra 87.94%.
Benchmarks
StepFun publishes its results as charts on the launch page. BenchGecko has no benchmark cells and no Gecko Tests for this model yet.
Sources
- Step 5 Preview on Hugging Face
- Step 5 Preview launch page
- Inside Step 5 Preview (StepFun technical blog)
- Step 5 Preview API docs
- BenchGecko model page: /model/step-5-preview
Source: BenchGecko
Written automatically from BenchGecko's tracked data for this period; every number comes from the changelog, model, mindshare and pricing datasets. Checked against the source data before publishing.