The most fuel-efficient Mercedes-Benz CLS63 AMG is the 2016 Mercedes-Benz CLS63 AMG S which gets 16 MPG City and 22 MPG Highway.
It is important to remember factors such as driving style, weather conditions, and the use of features such as Eco mode can impact fuel efficiency. Fuel economy figures are based on EPA estimates for when vehicle sold as new. Fuel economy may vary for reasons like driving conditions and vehicle history. Unless specified, figures are for vehicles equipped with an automatic transmission. See fueleconomy.gov.