It came down to the 11th hour, but both Variety and Hollywood Reporter's websites are saying that BL has been picked up for a 5th season. I think the negotiations had to do with ABC buying out "Life on Mars" from David E. Kelly, and in exchange, Kelley wanted at least another season of BL.
From what I've read elsewhere, it's a full-season, but ABC has the option to trim it down to 13 episodes.
I'm hugely disappointed that Annie had a gun and there was not a single Annie Get Your Gun musical reference. I want Evil Troy and Evil Abed to come back. Was Britta imitating Jar Jar Binks? Chops busted, fellow adult. Chops busted.