With the 2011 America Invents Act, the United States discarded its century-old first-to-invent patent-awarding system in favor of a first-to-file rule. Critics have argued that the first-to-file rule rewards speed in patent applications rather than creativity, thereby undermining innovation. We evaluate this concern within a dynamic model of a patent race, and find first-to-invent (weakly) more conducive to innovation than first-to-file. Defending prior users’ rights can promote both pro- and anti-R&D effect of a switch to first-to-file.