Dirk Nowitzki will likely opt out of the final year of his current contract, but don't worry, he probably isn't going anywhere. Several media outlets are reporting that Dirk will void the final year at some point next month.
Free agency opens on July first but that's not the real reason he's opting out. If he does this by the end of June, it allows him to negotiate a 4-year guaranteed deal with the Mavs under the current collective bargaining agreement.
Which means he could take less money immediately to help the Mavs sign another big name player but in the long run would make more money. Owner Mark Cuban has said before that he will do whatever it takes to keep Dirk in Dallas.