My Game Pass Ultimate expired yesterday, and I just renewed it with reward points. I got 4x 3 month Xbox Game Pass for PC codes at 20400 points each. It gave me an extra month for turning on recurring billing with the first code, I turned if off after, but didn't get offered it again, which is fair enough. I then ugraded with a 1 month Ultimate code for 12000 points.
So now I have 14 months to earn all those points back again, which will no problem. After paying for £200 of the cost of a Series S with points back in September, I've earned about 110000 points in the last 6 months, but that was with the 2 x 10000 points for gamerscore promos they did, so if those had not been available I would still have earned just enough points for those 14 months of Ultimate.