Step 5 Preview

Step 5 Preview is the flagship model from Shanghai-based StepFun, one of China's 'Six AI Tigers', launched in September 2026. It is a sparse mixture-of-experts model with 600B total parameters and 27B active, a 92-layer transformer design, a 1-million-token context window, and up to 64K output tokens with text, image, and video inputs. StepFun targets software engineering, professional knowledge work, and finance, reporting 66.4 on FrontierFinance and 67.7% on DeepSWE v1.1 in high-effort runs. API access began September 20, 2026, with open weights planned for October 15, 2026.

The honest picture: the headline benchmarks are company-reported with no independent verification at launch, and the open-weights release had not landed at the time of writing — 'planned' is not 'shipped'. Reported API pricing is $1.00/$2.70 per million input/output tokens, which is not cheap for a preview model, and StepFun's Western ecosystem presence is limited.