what should happen to a prominent app bar with long and two-lined title, when scrolling

In material design, if the title is long we should put it in a prominent Appbar like this:

The title should not be truncated or shrunk. so when the content scrolls up, should I transform the prominent Appbar to normal? If so, what would happen to the long title, as it should not be truncated or shrunk? Or we should let it be in this way all the time?