It's party time on CMT Hot 20 Countdown. Tune in as Carrie Underwood co-hosts and helps celebrate our 100th episode. We'll chat with Underwood about her new music, pregnancy and much more. Also on the show, this year's CMT Artists of the Year honorees -- Luke Bryan, Keith Urban, Jason Aldean, Florida Georgia Line and Miranda Lambert -- quiz one another. And we reveal the artist who earned the No. 1 spot on CMT's All-Time Top 40.