Juno and Cassini have transformed our understanding of the interior structures of the Solar System’s gas giants. Their gravity measurements suggest that both Jupiter and Saturn possess dilute, or "fuzzy," cores rather than traditional compact ones. This finding has profound implications for the transport of heat and heavy elements within giant planets, influencing their thermal evolution, luminosities, atmospheric metallicities, and present-day internal structures. 

In this talk, I present the first evolutionary models of Jupiter and Saturn that self-consistently incorporate fuzzy cores, helium rain, ammonia-cloud physics, and unified microphysics, while reproducing their thermal, compositional, and gravity constraints. I also quantify whether double-diffusive mixing can redistribute heavy elements and erode fuzzy cores over gigayear timescales. Finally, I will discuss how these insights extend to gas-giant exoplanets, highlighting similarities and differences relative to the heritage Sonora Bobcat model suite. By incorporating atmospheric mass loss into our evolutionary framework, we further investigate how the coupled evolution of planetary interiors and escaping atmospheres can shape the observed population of highly irradiated giant planets.