The Kenworth T660 was announced as the replacement for the T600. Retaining the cab and Aerocab sleeper of the T600, in a major shift, the T660 adopted diesel engines produced by PACCAR. For the first time since 1990, the aerodynamics of the hood and fenders were updated, as the T660 introduced composite headlamps faired into the fenders while adopting a grille similar to the T2000 conventional.

In 2016, Kenworth announced they were discontinuing the T660 in favor of the T680.