Right — if we can know how long ago the contracts were agreed we can predict how much more the price will have to rise, because 20% sounds like the beginning of the problem.
Apple is notorious for their prices being extremely stable for a given SKU. If anything, this is Apple getting out ahead of where they expect memory prices to be long-term, so they can rip off the band-aid once and don’t have to do it again.
I am personally working on the assumption that prices will go up again this year or say in January, though as I have an M1 Max here it's not massively urgent.