I was on one of the UA900s in Business Class not very long ago, they still had the old seats. There may be some aircrafts on that route that are equipped with the new lie flat seats. You would have to phone United and find out.
The same applied when I was on a flight from IAD
a couple of weeks ago. They had the old seats in Business Class also. The flights from IAD
(Argentina) always had the new seats in Biz and First in the 767-300s. I guess they must keep the new seats for longer routes, like Transpacs and flights to Brazil/Argentina.