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StepFun Launches Step 5 Preview: A 600B-Total, 27B-Active MoE Model With 1M Context ...
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Fusion42 · 21 September 2026 · Fusion42 review
StepFun launched Step 5 Preview, a 600 billion parameter Mixture-of-Experts (MoE) AI model with a 1 million token context window supporting text, image, and video inputs. The model targets software engineering, knowledge work, and finance workloads with competitive cost efficiency and will have open weights available from October 15, 2026.
This Wire brief sits within Fusion42's coverage of AI Frontier Models and AI Infrastructure, and 1 source has reported it.
◆ ◆ The Wire takeaway
StepFun's low-cost, long-context MoE model shifts your options for agentic AI in software and finance. Prepare infrastructure now to leverage open weights releasing mid-October and gain cost advantages in complex agent tasks.
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1 source · 21 Sep 2026
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