According to the press statement, the first half of the series will air in the spring, with the second half set to air in the fall.
This is what the BBC said:
The split transmission is the result of a request from Steven Moffat to write a new Doctor Who story arc which involves a big plot twist in the middle of the series. By splitting the series Moffat plans to give viewers one of the most exciting Doctor Who cliffhangers and plot twists ever, leaving them waiting, on the edge of their seats, until the autumn to find out what happens.Right now all I can think to say is Noooooooo. I hate cliffhangers and I hate being made to wait months to resolve a story. Personally, I'm quite disappointed with this decision to split the season in half and make us wait months again to see the rest of the series -- and I'm not so sure that it will turn out to be a good move.
Steven Moffat said: "The split series is hugely exciting because viewers will be treated to two premieres, two finales and more event episodes. For the kids it will never be more than a few months to the next Doctor Who! Easter, Autumn, Christmas!!"
But what do you guys think about the BBC and Steven Moffat's decision to split series 6 of Doctor Who in two? Good or bad idea?
[BBC Press Office]