From the press release.
Episode 1706” – Eight remaining couples hit the dance floor and face an exciting new challenge on “Dancing with the Stars,” MONDAY, OCTOBER 21 (8:00-10:01 p.m., ET).Each couple will compete in an individual dance style they have not yet done as well as take part in the first ever “Switch-Up Challenge.” In this fresh take on a dance marathon, couples will compete side by side, in two rounds, with no prior knowledge of dance style or musical accompaniment. One by one, the judges will select couples to be tapped-off removed from the dance floor. Extra judges' points will be awarded to couples based on longevity. The show will also feature a spectacular opening numberwith the entire cast, choreographed by Lacey and Benji Schwimmer. Additionally, musical guest Ariana Grande and Mika will perform their hit duet “Popular.” At the end of the night, one couple will face elimination.
Hosted by Emmy® Award-winning host Tom Bergeron (“America’s Funniest Home Videos”) and Brooke Burke-Charvet (“Dancing with the Stars” Season 7 Champion), “Dancing with the Stars” is the hit series in which celebrities perform choreographed dance routines which are judged by renowned ballroom judge Len Goodman and dancer choreographers Bruno Tonioli and Carrie Ann Inaba.
Viewers may cast their votes for their favorite teams via phone on Monday nights during and up to 60 minutes after the end of the “Dancing With the Stars."