❯ StepFun releases Step 5 Preview, a 600B-parameter MoE with a 1M context window

the releaseStepFun released Step 5 Preview, a mixture-of-experts model with 600B total parameters and 27B active, a 1 million token context window and vision capability, positioned by the company for software engineering and finance tasks. It is already live on StepFun’s own platform.

the trade-off600B total against 27B active is a configuration weighted clearly toward inference cost: the capability ceiling scales with total parameters while per-call spend scales with active ones. Paired with a 1M context and vision, it points at long-document-plus-chart professional work — financial research and large codebases are exactly the tasks with the longest contexts. Until now the main models in this parameter band from China’s open camp came from DeepSeek and Z.ai.

reading itCalling it a Preview and publishing no third-party benchmarks makes this look more like a capability trailer than a shipped product. For teams doing model selection, the only certainties right now are the architecture and the context length; real comparison waits on independent evaluators publishing an intelligence index and a cost per task. Before those two numbers land, this is a calendar note at best.

▪ SIGNAL600 billion total against 27 billion active — Chinese models chose the inference bill over the capability ceiling.