The Thule EasyFold XT 3 bike carrier is designed to transport up to 3 bikes as standard and there is no official extension or adapter from Thule to extend it to 4 bikes.

A similar model, the Thule VeloSpace XT, can be extended to 4 bikes with an adapter, but this does not apply to the EasyFold XT 3, so an extension of the EasyFold XT 3 to 4 bikes with an adapter is not intended or officially supported.