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