Alexander returned to IMSA in the USA to make his debut in the prototype class, racing the Cadillac V-Series.R prepared by Action Express Racing alongside Pipo Derani.
Having won in Sebring, Sims secured third place podium finishes at Laguna Seca and Watkins Glen en route to claiming the overall drivers and teams Championships alongside Derani, with the pair teaming up with Jack Aitken to claim the overall Endurance Championship.