"I'm really happy to know where I'm going to be for the next 15 years,” the $765 million man told media on Sunday.
Initial speculation has Bregman playing second base in Boston, despite being a Gold Glove winner at third.
Pitching more efficiently and getting ahead in counts are also priorities for the second-year ace.
Ohtani likely won't face opposing hitters during spring training and isn't expected to pitch in a game until May.