Back when points reservations were based on a category chart, the program was called "Fifth Night Free." That's not what it is now.

With dynamic points, the nights of a 5-night stay are seldom the same each night. The program is now called "Stay for 5, Pay for 4." As others have noted, you pay for the most expensive four nights. Then, the least expensive night is zero points.

Also, it's only free if you pick the standard redemption. If a standard redemption is 50,000 points, but a suite redemption is 80,000 points, and you pick 5 nights in a suite, then the free night still costs 30,000 points for the upgrade.