Season 13

The thirteenth season of It's Always Sunny in Philadelphia has been officially commissioned by the FXX network and premiered in September 2018 FXX. The first episode aired on September 5th, 2018. It consisted of 10 episodes.

News
On April 1, 2016 it was announced that FXX commissioned season 13 and season 14 of Sunny, tying it for the longest-running live action television comedy in American television history.

In an interview published on March 8, 2017, Glenn Howerton stated that there may be an "extended hiatus" before season 13, and that he may not return to the show: "We may be taking an extended hiatus between season 12 and season 13. So I’m certainly staying open to the possibility of doing more, but there is a possibility that I will not."

In an interview with TV Guide, Kaitlin Olson confirmed that the show will take an extended hiatus to accomodate the cast's other projects: "We ended up pushing our next season a year because we were all busy with separate projects this year. So at the end of this coming shooting season of  The Mick  I'll step right into  Sunny  after that."

On April 7, 2018, Kailtin Olson posted the following to her Instagram account, next to a picture of a bird with Sweet Dee's head:

kaitlinolson Two more weeks until we start shooting season 13 of this lady and a few other guys. #ItsAlwaysSunnyInPhiladelphia #FXX #season13

She also confirmed in an interview with The Wrap that Glenn Howerton will be back for at least a few episodes as Dennis: “I do know that Glenn Howerton is coming back for some episodes...I don’t know the specifics, but I do know how he’s being introduced back in, and it is absolutely hilarious.”