Two Convertibles with some similarities, but otherwise different in most aspects such as the model year, horsepower, fuel economy, ground shadow size, and height. First of all, the is a newer vehicle by 3 model years. Also, the 2021 718 Boxster has bigger and thirstier engine; the 2018 4C Spider gets 5.5 more mpg. And finally, the 4C Spider is both slightly smaller and shorter than the 718 Boxster. Among similarities are the body structure, market segment, starting price, and maximum occupancy.