Well, Sarah tweeted about it so it must be official. She will be hosting Saturday Night Live on October 4, the second episode of the 40th anniversary season. This will be her first time at SNL since she worked on the show during the 1993-1994 season.
Several posts went up yesterday about the news but were quickly deleted, apparently because they were also reporting that Bill Murray would be hosting the September 27 season premiere. That turns out to have been premature; the host is now being announced as Chris Pratt (of Guardians of the Galaxy), although there is still speculation that Murray will show up sometime during the coming season.
Along with Sarah will be musical guest Maroon 5.