The mirroring hypothesis is central to modularity theory, positing isomorphism between technical interdependencies of a product and organizational arrangements. When a product’s design becomes more modular, a full mirroring response would change both its manufacturing and its supply chain. We evaluate this prediction for Battery Electric Vehicles (BEVs), observing whether automakers have mirrored the modular BEV architecture in either internal production processes, external sourcing arrangements, or both. Our data from 19 automakers show that, to date, BEVs are manufactured in their assembly plants alongside conventional internal combustion engine vehicles (ICEVs). New automakers with fully BEV plants utilize essentially the same production process. Furthermore, automakers make—or ally to make—key Electric Vehicle (EV) systems, rather than outsourcing them. We discuss the implications of this partial mirroring for modularity theory and ask whether these arrangements will persist once BEV sales surpass ICEVs.