On the morning of September 20, StepFun unveiled its next-generation flagship foundation model, Step 5 Preview, designed specifically for AI coding, software engineering, professional knowledge work, and financial applications to elevate its overall performance in real-world agentic tasks. The model achieves a well-calibrated balance between capability, cost, efficiency, and scenario coverage, further pushing the optimal frontier between intelligence and expenditure.

On the globally recognized Artificial Analysis Intelligence Index (AA Composite Intelligence Index), Step 5 Preview has clinched a spot among the top three open-source models worldwide. Notably, the single-task cost of this model is only one-eighth that of Claude Opus 5. StepFun has confirmed that Step 5 Preview will be officially open-sourced on October 15.

Step 5 Preview employs a sparse MoE architecture, with a total parameter count of 600B and only 27B active parameters, supporting a 1 million-token context window and natively accepting both text and visual inputs. It excels in software engineering, professional workflows, and financial contexts. Positioned for real-world agentic tasks, the model serves as a reliable workhorse for sustainably handling complex operations.

In the trade-off between capability and cost, the "Pareto frontier" often describes the optimal boundary currently attainable. The further the frontier expands outward, the stronger the intelligence purchasable at the same price. Step 5 Preview brings the balance between Intelligence Index and per-task cost closer to a more favorable solution.