Even though Sunday's Survivor finale was the least-watched wrap-up in the show's history, CBS is planning at least three more seasons of deprivation and backstabbing. The network has reviewed broadcast TV's longest-running primetime reality series through Season 12, which will air in spring 2006. Still, producer Mark Burnett plans to shake up the show in upcoming seasons; it's already been revealed that the 10th season this fall will feature 20 competitors instead of 18. ''It's a completely new take on how to begin Survivor,'' he tells Variety. There will be other changes, which Burnett is keeping secret for now. As long as they don't involve integrating Paris Hilton into the show, Survivor fans will surely keep watching.