Agentworld begins from the proposition that technological capacities have outrun the concepts available to describe them. Its object is not artificial intelligence as a tool but the diffusion of artificial agents into densely reticulated human–machine societies. Bratton imagines a world in which nonhuman human-level minds vastly outnumber human ones, producing nested social systems whose languages, hierarchies, institutions and lifeworlds evolve through reciprocal adaptation. The iconic figure is the centaur society: neither human society supplemented by machines nor autonomous machine civilisation, but a hybrid ecology in which each population becomes the evolutionary niche of the other. The method is preemptive anthropology, using speculative scenarios to develop conceptual frameworks before the social forms they address become fully stabilised. Agentworld bridges philosophy of technology, anthropology, artificial intelligence and institutional design by treating agency as an open-world ecological problem. Its contribution is to move debate beyond task completion and alignment toward the symbolic, psychological and political realities of societies populated by heterogeneous minds.