A LinkedIn resume of a senior animator at 2K Games lists work on BioShock Infinite downloadable content. The interesting thing about this is that it mentions “providing animation and R&D for a new AI companion character”.
Irrational Games received a lot of praise for making Elizabeth a believable and useful companion character for Booker, many saying she is among the best ever seen in a game. You never have to worry about her dying mid battle and she regularly supplies you with cash, health and salts. So fans will be happy to hear that it seems there will be another character with similar usefulness appearing in the DLC.
No specific release date has been confirmed as of yet but we can expect this to change over the coming months. There will be 10 new achievements to earn according to a recent leak
Further to this we know there are two pieces of story-related content planned, in addition to costumes, weapons and item upgrades, all of which are included in the Season Pass.