Long term has been answered, I think. Short term, though, really is tank. No, he'll never say that and will adamantly deny the very thought of intentionally losing at every opportunity. What I think he's going to do, though, is make sure the roster that Coach Stevens has to work with is composed of almost only young developmental players who try their best and still lose a lot of games.
The Celtics won't intentionally lose any games, they'll play their hearts out and earn every loss. I expect them to play themselves to the 7th or 8th pick in the draft.