tl;dr: SpaceX's Raptor engine has evolved from a tangle of external pipes and wires (v1) to a streamlined v3 with 35% more thrust, while retaining the same full-flow staged combustion architecture. Key changes include removing development sensors, eliminating main chamber igniters and helium systems, replacing bolted flanges with welded joints, consolidating small lines into a common umbilical, and using 3D printing to internalize plumbing—which allowed removal of the heavy external heat shield. Much of this is pieced together from Musk's tweets and enthusiast speculation, as SpaceX hasn't released official schematics.