Ideally no one, and if the cost / expertise is so niche that only a handful of sophisticated actors could possibly actually do it, then in fact (by way of enforceable treaty) no one.
Anyone who wants to establish deterrence against superiors or peers, and open up options for handling weaker opponents.
> enforceable treaty
Such a thing does not exist. International affairs are and will always be in a state of anarchy. If at some point they aren't, then there is no "international" anymore.
> enforceable treaty
How would you enforce it after you get nuked?
We're talking about making war slightly more expensive for yourself to preserve the things that matter, which is a trade-off that we make all the time. Even in war you don't have to race for the bottom for every marginal fraction-of-a-percent edge. We've managed to e.g. ban antipersonnel landmines, this is an extremely similar case.
> How would you enforce it after you get nuked?
And yet we've somehow managed to avoid getting into nuclear wars.
AI on the other hand seems to be very multi purpose
Feels good but will lead to disaster in the long run.
Yes, through a massive programme of nuclear armament. In the case of AI, we should therefore...?