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Physix Frontier · News Briefing Card (QbitAI · Sep 21, 2026)

StepFun Releases Step 5 Preview, New Open-Source Value Leader

KEY FACTS

  • StepFun has launched Step 5 Preview, featuring a MoE architecture with 600B total parameters but only 27B active.
  • The model scored 44 points in Artificial Analysis evaluations, ranking second among global open-source models.
  • Pricing is highly competitive at $1 per million input tokens and $2.7 for output, costing just 12.5% of Opus 5.
  • Real-world tests show significantly improved agent capabilities, enabling autonomous completion of complex tasks like 3D modeling and game development.

KEY DATA

600BTotal Parameters
27BActive Parameters
44 ptsAA Evaluation Score
12.5%Cost Relative to Opus 5

PHYSIX OBSERVATION

StepFun’s 'narrow and deep' architecture shatters the scaling myth that relies solely on parameter count, proving that small active parameters can support long-horizon agent tasks. This marks a shift in LLM competition from leaderboard rankings to optimizing the performance-cost Pareto frontier, forcing the industry to re-evaluate inference efficiency and deployment economics while offering high-value productivity tools for smaller teams.

Source: QbitAI report