Stolarz made his senior international debut at the 2021 IIHF World Championship, starting Game 1 in goal for the United States. He suffered an ankle injury five minutes into the first period of the first game, however, and had to be replaced by backup goaltender Jake Oettinger. On May 25, 2021, it was announced that Stolarz would not return for the remainder of the series. Team USA took bronze in the tournament after defeating Germany in the finals.