Those weapons are still all being developed and would be brought out in any actually existential war where they seemed useful. The agreements would last only as long as the wars were not existential, or as long as the various countries involved believed that use of them, and the resulting retaliation in kind, would be more destructive than not using them. But one way or another, countries still develop them.

China is rapidly building out their nuclear arsenal as we speak, and the USA is undergoing an expensive replacement process of theirs as well.

That kind of idea might have held water in the 90's, but that's not the world we live in any longer.

> Haven't many (most?) countries agreed to nuclear disarmament?

This misses the point. He specifically said the entire world because the point is that someone will develop AGI (theoretically; I’m not making a statement about how close we are to this).

9 nations have nuclear weapons despite non proliferation agreements and supposed disarmament. It’s not enough for most countries to agree not to build nuclear weapons if the goal is to have no nuclear weapons. Same for AGI. If it can be developed, you need all nations to agree not to develop it if it don’t want it to exist. Otherwise it will simply be developed by nations that don’t agree with you.

(Also arguably the only reason most nations don’t have nuclear weapons is the threat of destruction from nations that already have them if they try.)