This is a pivotal phase study of up to 120 subjects and 15 clinical sites. All subjects are implanted with the Vivistim System® and then randomized to either study treatment or active-control treatment. The randomization will be stratified by age (<30, >30) and baseline FMA UE (20 to <35; >35 to 50). Study treatment is vagus nerve stimulation (VNS) delivered during rehabilitation. Active control treatment is rehabilitation (standard-of-care treatment) with only a minimal amount of VNS at the start of each session intended to support blinding.