Step 5 Preview brings 600B capacity to 27B active parameters
StepFun’s Step 5 Preview gives agent builders a 600B-parameter model that activates 27B parameters per token, with a 1M-token context window and vision input. Its sparse Mixture-of-Experts design routes each token through only part of the model, while StepFun reports scores of 67.7 on DeepSWE v1.1, 49.0 on StepCodeBench, and 80.5 on ProgramBench. Those results beat Kimi K3 Max on all three listed tests.