Looks like the PS3-exclusive multiplayer Beta for Assassin's Creed Brotherhood is a GameStop pre-order exclusive in the US.
Pre-order it anywhere else and it's no Beta for you, apparently.
According to the press release, Ubisoft and GameStop will issue a limited number of tokens for the Beta on a "first-come, first-served" basis starting August 9.
Already pre-ordered Brotherhood through GameStop? Just show head on down to your nearest store your receipt to the clerk and get yourself a token.
The Beta starts on September 19, and the game itself releases on November 16 in the US and November 19 in the UK for PS3, 360 and PC.