China's StepFun released its newest flagship agentic AI model with a 1 million token context window and vision capabilities. This model, known as Step 5 Preview, utilizes a Mixture-of-Experts architecture with 600B total parameters and 27B active parameters. It achieved a score of 44 on Artificial Analysis, matching the Kimi K3 (max) while operating at a 65% lower cost per task.

The model is currently available via API at $1.00 per 1M input tokens and $2.70 per 1M output tokens. StepFun will release the open weights on Oct 15, targeting professional knowledge work in software engineering and finance. The architecture is designed to support sustained execution over long horizons for complex agentic tasks.