StepFun's Step 5 Preview is a proprietary reasoning model with 600B parameters released September 18, 2026, scoring 44 on the Artificial Analysis Intelligence Index with competitive pricing of $1.00 per 1M input tokens and $2.70 per 1M output tokens. The multimodal model supports text and image inputs, offers a 1M token context window, and ranks well above average in intelligence compared to similarly priced models.