StepFun Launches Step 5 Preview, a Frontier Model Targeting Cost-Capability Pareto Frontier
omarsar0 · x · 2026-09-21
StepFun has released Step 5 Preview, its new-generation flagship model, positioned as "advancing the Pareto frontier" — i.e. optimizing the trade-off between cost and capability.
- A Step Plan subscription was introduced alongside it, covering flagship-model access from coding to agentic workflows.
- The voice line was refreshed with StepAudio 3: ASR, Realtime voice interaction, voice generation, and music generation.
- The platform offers a unified API where one key covers language, speech, and vision models, and is compatible with the OpenAI SDK (baseurl at api.stepfun.ai/v1).
- There is also a no-code Studio, plus developer and startup programs offering tokens and technical support.
AI researcher Omar Sanseviero, who tested it early, called it impressive: used as a coding agent it sits on the cost-vs-capability Pareto frontier, is comparable to GLM 5.3 and Kimi K3, and comes at a very competitive price — worth trying in your favorite coding agent.
Related event: StepFun Surprises with Step 5 Preview, Touting Cost-Performance Frontier(4 posts)→
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