Step 5 Preview officially arrived on Tencent's WorkBuddy on October 12, 2026, with StepFun announcing the same day an exclusive free-access window on WorkBuddy from October 12 to October 25. The flagship foundation model, first released on September 20, steps into an office workbench first and only then open-sources its full weights on October 15 as planned — the order itself shows that StepFun wants real office users and feedback before it hands over the weights.
600B total parameters, only 27B active
Step 5 Preview uses a sparse MoE architecture with 600B total parameters and about 27B activated per token, supports a 1M-token context window and native text-plus-vision input, and is tuned for AI coding, software engineering, professional knowledge work and finance. On the Artificial Analysis Intelligence Index it ranks among the top three open models worldwide, and StepFun puts its cost per task at roughly one eighth of Claude Opus 5. Its positioning is not the biggest model, but a workhorse that can keep working through long tasks at a contained cost.
Why WorkBuddy first, and the open release second
WorkBuddy is Tencent's all-scenario AI office workbench, where users handle documents, spreadsheets and everyday office tasks — precisely the professional knowledge work Step 5 Preview targets. For StepFun, the exclusive free window is a low-cost, large-scale test on real tasks: office users do not ask questions the way benchmark suites do, and file formats, context lengths and multi-step jobs expose a model's weaknesses directly. For users, the two weeks are equally concrete: no API setup and no payment, just their own real documents and spreadsheets to test the gap against their current tools. The change in long-context capabilities can also be read alongside this site's earlier report on GPT-6.1 Sol's default context rising to 500k.
What to watch after the free window and the weights
Once the full weights are open-sourced on October 15, the yardstick changes: actual memory footprint and inference speed in community deployments, whether enterprises dare to wire it into internal workflows, and whether WorkBuddy users stay after the free period ends. A flagship model entering an office platform is no longer rare; what is rare is turning free usage into sustained calls. October 25, when the free window closes, is the concrete date this story leaves readers: anyone who wants to try it should do so within the window, with real tasks, rather than wait for leaderboards.
