What,
two days ago, was a news item that existed somewhere between "rumor" and "official," is now 100% official with the announcement by Gearbox and 2K Games that
Borderlands 2 will, indeed, get a fifth class that's known as the Mechromancer. Gearbox says they won't even begin work on it until after
Borderlands 2 is finished and in certifications (2K states
right here that is will be between 60 and 90 days after the game is released before the Mechromancer becomes available), so it's possible some of the details could change once the Mechromancer moves out of the concept stage.
Furthermore, whenever it's released, it will be free to members of the
Borderlands 2 Premier Club. Fortunately, one can attain membership in the
Borderlands 2 Premier Club simply by pre-ordering the game at participating retailers (read the full list of participating retailers
right here).
Right now, all that's known about the Mechromancer is that she can control D374-TP or "deathtrap" mech which can be seen below, along with concept art for the Mechromancer herself, in case you missed it before.