Aguilera last performed on the show in 2007. It's the second time for New Kids and Bastille. It's Dan and Shay's first appearance. Seacrest will be joined in the countdown to midnight by Jenny McCarthy Wahlberg.
Post Malone will make his first New Year's performance. Ciara will host the Hollywood party with such artists as Camila Cabello, The Chainsmokers, Halsey, Shawn Mendes, Charlie Puth and Weezer. The show begins at 8 p.m. on Dec. 31 on ABC.