Back in February a pretty major devaluation of the Marriott Rewards program was announced. The changes consisted of them adding a ninth hotel category, and 36% of properties going up at least one category.
Anyway, the changes kick in on May 16, so if you want to lock in any award nights at the old levels, this is your last chance. You can find a full listing of the categories here to get an idea of whether a property you’re eying goes up in price or not.
It’s worth keeping in mind that Marriott will let you make a reward booking even if you don’t have enough points in your account. So even if a stay is only speculative at this point it can make sense to lock it in, though just be sure you’re familiar with the cancellation policy for the property you book.