When does It's Always Sunny in Philadelphia return?

The series follows the exploits of "The Gang", a group of narcissistic and sociopathic friends who run the Irish dive bar Paddy's Pub in South Philadelphia, Pennsylvania. It premiered on August 4, 2005, and was moved to FXX beginning with the ninth season in 2013. With its fifteenth season, the series became the longest running live-action American sitcom, surpassing The Adventures of Ozzie and Harriet, which ran for 14 seasons between 1952 and 1966.
The series follows a group of misfit, narcissistic sociopaths, referred to "The Gang", who run a meager, unsuccessful Irish bar called Paddy's Pub in the neighborhood of South Philadelphia. The Gang originally consists of janitor Charlie Kelly (Charlie Day), bouncer Mac (Rob McElhenney), and bartender Dennis Reynolds (Glenn Howerton) The Gang is joined by Frank Reynolds (Danny DeVito), an eccentric millionaire and the neglectful father of the Reynolds twins, who takes over most of the ownership of the bar.