Independence

How few parties have to agree before this works at all?

A solution one country can enact alone is worth more than one that needs a global treaty, because treaties are where good ideas go to wait.

The scale

1. 1Genuinely global treaty
2. 2All major AI powers
3. 3A bloc of allies
4. 4A single state
5. 5One actor acting alone

Five is the good end on every criterion, so no row reads backwards.