Apple says the following models are eligible:
MacBook (Retina, 12-inch, Early 2015)
MacBook (Retina, 12-inch, Early 2016)
MacBook (Retina, 12-inch, 2017)
MacBook Pro (13-inch, 2016, Two Thunderbolt 3 Ports)
MacBook Pro (13-inch, 2017, Two Thunderbolt 3 Ports)
MacBook Pro (13-inch, 2016, Four Thunderbolt 3 Ports)
MacBook Pro (13-inch, 2017, Four Thunderbolt 3 Ports)
MacBook Pro (15-inch, 2016)
MacBook Pro (15-inch, 2017)