In a new interview with iFMagazine, the legendary actor Sir Ian McKellen has confirmed his involvement with The Lord of the Rings prequel, The Hobbit, indicating:

I have been promised I’m in it.

This happened 12 hours from eating dinner with The Hobbit director Guillermo Del Toro. He also mentioned that it’s possible that he will reprise [...]

Del Toro confirmed, in an interview with BBC Radio 5, that Hugo Weaving will reprise the role of Elrond in the upcoming Hobbit films. Also he confirms that Andy Serkis will reprise Gollum and Ian McKellen will reprise Gandalf.
Thanks EW!

A few days ago in an interview with iFMagazine, Ian McKellen (Gandalf) talks about The Hobbit and he say
“I’m having supper with [director] Guillermo del Toro this evening, so you’re asking me twelve hours too early.”.
Also he already confirm that he will be in The Hobbit.