The special will feature characters from Facts of Life and Diff'rent Strokes. Aniston will play Blair (originally played by Lisa Whelchel), with Union as Tootie (Kim Fields), Hahn as Jo (Nancy McKeon) and Tolman as Natalie (Mindy Cohn).
Ann Dowd was previously announced as Mrs. Garrett (Charlotte Rae). John Lithgow will play the Diff'rent Strokes character Mr. Drummond (Conrad Bain), with Kevin Hart as Arnold (Gary Coleman) and Damon Wayans as Willis (Todd Bridges).
Kimmel, Norman Lear, Brent Miller, Kerry Washington, Will Ferrell, Justin Theroux and Jim Burrows will executive produce the special, with Burrows and Andy Fisher to direct the show.
Diff'rent Strokes was created by Jeff Harris and Bernie Kukoff and had an eight-season run from 1978 to 1986, while The Facts of Life was created by Dick Clair and Jenna McMahon and aired for nine seasons from 1979 to 1988.
ABC previously aired Live in Front of a Studio Audience specials that recreated episodes of All in the Family, The Jeffersons and Good Times.
The new special will air Dec. 7 at 8 p.m. EST on ABC and stream on Hulu the next day.