NBC has renewed Community for a 13-episode fourth season, as per The Hollywood Reporter. The deal is not for a final season, like the deal for 30 Rock announced earlier today, but there is no news on whether or not there will be the potential for more episodes if the show exceeds expectations (or simply performs slightly better than the new comedies on the network). Presumably, that information will become more clear when NBC announces whether the show will be on in the fall or will be pushed to midseason (which would make a full back nine order more difficult). If it aired in the fall, Community would become, in effect, one of NBC's new shows, competing with them all to be one of those picked up for the back nine. There is precedent for this in recent NBC history, with Chuck receiving a 13-episode pickup for its fourth season, an order that was increased by 11 episodes when the episodes that aired in the fall over-performed expectations. (The spring episodes then quickly sank into the ratings toilet.)
In the meantime, in case you need something to freak out about, this Deadline report on the renewal suggests there exists a possibility Dan Harmon will no longer be the series' showrunner. With executive producers Neil Goldman and Garrett Donovan exiting for their deal with Fox, that would leave a big vacuum on the show (unless Harmon stepped down as showrunner but continued to be the series' head writer somehow). Since the Deadline report suggests this is just one of many possibilities, we will choose to ignore it and be happy about the renewal news.