When Marriott Bonvoy made announcements about the combined program back in 2018, seasonal award pricing was set to be introduced in early 2019. Marriott further clarified month ago that these would now be effective on September 14, 2019.
Marriott Bonvoy is changing how Points Advance (award reservations for which the member doesn’t have enough points in his/her account) are processed. You can lock in the award space but not the price using points. The number of Points Advance reservations that each member may have outstanding is reduced.