Not clear what you mean.
Do you mean it is generic to do that in contracts? (Been a while since I was offered equity.)
Or do you mean that even OpenAI would not try it without having set it up in the original contract? Because I hate to be the guy with the square brackets ;-)
Normally a company has to give you new "consideration" (which is the legal term for something of value) for you to want to sign an exit agreement - otherwise you can just not bother to sign. Usually this is extra compensation. In this case they are saying that they won't exercise some clause in an existing agreement that allows them to claw back.
Joke aside - I'm saying "it must" the same way someone might say "surely".