To be clear, there is no official confirmation about this, so take it with a grain of salt. A post going around Tumblr right now is claiming that in the introduction for comedian John Mulaney's set at NYC's Comedy Cellar last night, it was announced that he is replacing Seth Meyers as the new head writer at Saturday Night Live. If that's true, it's really the perfect choice—this is, after all the guy who co-created Bill Hader's Stefon.
More factors to consider: NBC just passed on his new show, Mulaney, so it's not out of the realm of possibility that Mulaney would return to SNL to take Meyers' place. On the other hand, Meyers told the Today show last month that he would be returning to SNL for the first half of the season—until February 2014—before he heads off to take Jimmy Fallon's place at Late Night, so it's possible we won't have any official word on his replacement for a while.
We'll have more information about this as it becomes available.