Capcom has said Street Fighter x Tekken will be released in the fall on Vita, and when it hits, it will contain 12 additional characters.
The additional characters from the Street Fighter series are: Blanka, Cody, Dudley, Elena, Guy and Sakura, and the additional Tekken characters are: Alisa, Bryan, Christie, Jack, Lars and Lei.
It's unclear at present whether these characters will be added to the console and PC versions at this point, or whether the pack will be released as paid or free DLC.
So, its' a maybe, then.
Street Fighter x Tekken releases March 6 in the US and March 9 in Europe on PS3 and Xbox 360.
A PC version is due in May. Thanks, Andriasang.