The production begins in mid-July, and the first episode will air on FOX (USA) on the 19th of September 2013.
So get ready for a lot of changes, especially in the cast. For instance, Jacob Artist (Jake), Melissa Benoist (Marley), Blake Jenner (Ryder), Alex Newell (Unique) and Becca Tobin (Kitty) - a.k.a. the 4th season "newbies" - will now join the main cast :)
However, Amber Riley (Mercedes), Heather Morris (Brittany), Mark Salling (Puck) and Harry Shum Jr. (Mike) will become recurring casts :(
So ... RDV on the 19th of September, in front of your TV screens :)