Although there are some similarities, these two are different in most aspects such as model year, body structure, powertrain, horsepower, fuel economy, market segment, and ground shadow size. First of all, there is a difference in model years. The is 3 years newer. Also, a major difference is in the body structure and in the size of the vehicles. The 2018 Clarity Plug-in Hybrid is a Sedan and is slightly larger than the 2021 Ioniq Electric, which is a Hatchback. In addition, the Clarity Plug-in Hybrid has bigger and thirstier engine; the Ioniq Electric gets 13 more mpg. Among similarities are the starting price and maximum occupancy.