StepFun reportedly launches Step 5 Preview, a ~600B MoE model with 1M context and open weights due Oct 15, Pandaily reports
Reported by Pandaily · not yet confirmed by the company or a second independent outlet. We update this page when it is.
StepFun launched Step 5 Preview on September 20, 2026: a ~600B sparse MoE (~27B active) with 1M context for long-horizon agents, API live now and BF16 open weights planned for October 15, Pandaily reported.
China context
- Original name
- 阶跃星辰
- Outside China
- Not stated in the sources yet
- Claims
- Company-reported; not yet independently evaluated
- For builders
- Builders outside China can plan to evaluate the open weights on October 15 for long-context agent applications, but should verify actual availability and license terms.
- For investors
- Investors should monitor whether StepFun's open-weights release pressures other Chinese labs to accelerate their own open-source long-context models.
StepFun launched Step 5 Preview on September 20, 2026, a ~600B sparse mixture-of-experts model with ~27B active parameters and 1M context length, targeting long-horizon agent tasks. The API is live now, and BF16 open weights are planned for October 15, according to Pandaily.
The model uses a sparse mixture-of-experts architecture with approximately 600B total parameters and 27B active parameters, enabling efficient inference for long-context agent workloads. The 1M context window supports long-horizon tasks, and the planned BF16 open weights release on October 15 will allow independent evaluation.
Developers outside China gain access to a high-capacity open-weights model with 1M context on October 15, potentially reducing reliance on proprietary long-context APIs. Competitors must assess whether Step 5 Preview's agent performance matches or exceeds existing open models like DeepSeek or Qwen.
StepFun's Step 5 Preview offers a cost-efficient option for long-context agent applications due to its sparse MoE design, with open weights enabling self-hosting and fine-tuning. The API is available now for immediate integration.
The key signal to watch is whether StepFun releases the BF16 weights on October 15 as planned, and whether independent benchmarks confirm the model's long-horizon agent capabilities. API adoption and developer feedback in the first month will indicate real-world performance.