StepFun opened API access to Step 5 Preview, a sparse mixture of experts model with 600 billion total parameters and 27 billion active per token, taking text and images. Artificial Analysis scores it 44 on its intelligence index, 24th of 200 models, at $1.00 per million input tokens and $2.70 per million output, with output running at about 100 tokens a second. The weights are not published. Listings disagree about the context window, with Artificial Analysis and StepFun's own API giving 1M tokens and some trackers repeating 100K, so the figure is recorded as reported rather than resolved.