From the Warner Brothers press release:
“Despite the various rumours and speculation surrounding this role, there has only ever been one Bilbo Baggins for us,” says Peter Jackson. “There are a few times in your career when you come across an actor who you know was born to play a role, but that was the case as soon as I met Martin. He is intelligent, funny, surprising and brave - exactly like Bilbo and I feel incredibly proud to be able to announce that he is our Hobbit.”
THERE HAS ONLY EVER BEEN ONE BILBO BAGGINS FOR US
OMG IT’S CONFIRMED? YES YES YES