Hartlieb was claimed off waivers by the Red Sox on Saturday, Tim Healey of Newsday reports.
Hartlieb was designated for assignment by the Mets on Thursday, but he'll join Boston's 40-man roster. The right-hander had been pitching at the Triple-A level before he was DFA'd, and the Red Sox will have to make an additional roster move if they intend to bring him up to the majors.