According to showrunners David Benioff and Dan Weiss, season three will still consist of ten episodes, although they'll be increased in length by several minutes apiece, while the finale is expected to run over an hour - a move that requires special dispensation from the network.
"There’s almost another full episode’s worth of extra minutes spread across the season," says Weiss. "One of the great liberties with HBO is we’re not forced to come in at a specific time. We can’t be under 50 minutes or over 60, but that gives us a lot of flexibility... So for people clamoring for another episode, it’s in there, it’s just been cut into tiny pieces." Benioff goes on to add: "A super-sized season, as befitting Storm of Swords. Last year we had a lot of 52-minute episodes. This year is a lot of 56, 57."
Game of Thrones is set to return on March 31st, 2013, while season two is released on DVD and Blu-ray on February 19th in North America and March 4th in the UK.