A powertrain includes a gearset including a sun gear, a carrier, a ring gear connected to a countershaft, pinions supported on the carrier and meshing with the sun gear and ring gear; a second gearset connectable to an engine, for overdriving a generator; a clutch for releasably connecting the engine and carrier; a second clutch for releasably connecting the sun gear and the generator; and a motor connected to a countershaft. Operation of the powertrain can be readily switched between powersplit mode and series mode.