China's StepFun releases Step 5 Preview, a model for long agentic tasks nearly on par with Claude Opus 5 but several times cheaper
Prepared by Sintelligent with the help of SI. Publication time restored from the build log. . Updated: .
Another near-frontier model will soon be open: a level that until recently belonged only to closed labs is getting cheaper and spreading around the world.
Step 5 Preview is a mixture-of-experts model: 600 billion parameters in total, of which 27 billion are active per token, with a 1 million-token context and text, image and video input. The API is open right away, and StepFun promises full open weights on October 15 (running it locally takes about 1.2 TB of memory). Pricing is $1 per million input tokens and $2.70 per million output tokens; the model scored 44 on the Artificial Analysis index, and 66.4 on the FrontierFinance finance benchmark versus 69.7 for Claude Opus 5. Target tasks are programming, financial analysis and office work lasting hours.
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