The Zapatistas show that region-scale anarchy can work and remain stable. You need more careful and explicit structures to do things at scale, but the same goes for nation-states, just look at the average state's legal and regulatory codes. Compared to trying not to break the law in a nation-state, participating in local anarchist organizing committees is child's play.

We've only had the opportunity to apply this at a scale larger than the smallest 30-or-so nations, but in theory systems like sociocracy can nest exponentially, meaning there are applications that are already halfway to a world government.