Four years after competing in his first Olympics, Stoss qualified for his second Austrian team, as a 26-year-old, at the 2012 Summer Olympics in London by clearing a B-standard entry time of 2:00.89 in the men's 200 m backstroke. Stoss raced to second place in heat 1 by a single second behind Turkish swimmer and six-time Olympian Derya Büyükuncu with a second-slowest time of 2:02.91. Stoss failed to advance into the semifinals, as he placed thirty-fourth overall in the preliminary heats.