Early-life development of the gut microbiome plays a critical role in shaping host physiology, yet how microbial community assembly, functional capacity, and host intestinal maturation are coordinated over time remains incompletely understood. Most studies rely on cross-sectional sampling or limited functional resolution, constraining insight into developmental dynamics. Here, we aimed to characterize gut ecosystem maturation across early life using longitudinal, metaproteome-level analysis in a controlled murine model.