Suppose, you want to book a hotel room.
After seven days the reservation expires and you have to manually confirm the reservation. Hence, I call it an "expiring reservation".
After seven days the reservation also expires but is turned into a booking automatically. One would have to manually cancel the reservation before the due date.
I want a word for the second kind of reservation that conveys the meaning of "turns into a booking in the future unless you opt out". I thought about "future booking", yet I don't find it ideal. (It's not a booking, if you opt out there are no fees involved.)
I want a short wording that makes the distinction between these two types of reservations as clear as possible.