As Ranger wrote:
It has been confirmed that the exclusive beta will start on October 1, 2013, with the beta being available to everyone else on October 4, 2013 and ending on October 15, 2013. The map that will be featured in the beta is Siege of Shanghai on Conquest and Domination.
The "Exclusive" beta means that its avilable to those who are Battlefield Premium members in BF3, thoses who pre-ordered the BF4 Digital Deluxe pack, or those who pre-ordered MoH Warfighter (for whatever god aweful reason). See you on the Battlefield awyman13 Talk Work 20:19, August 20, 2013 (UTC)
Update: It has recently been announced that the Beta will be available for pre-download on September 28, 2013! That means that you dont have to wait when October 1st or 4th rolls around!