This essay sketches the class structure that a large-scale deployment of artificial intelligence might produce in advanced economies. Because AI is a general-purpose technology, its aggregate effects cannot be predicted, but three consequences can be reasoned through: output per unit of live labor will rise; a surplus population of the durably unemployable, potentially 15 to 20 percent of the labor force, may emerge; and the mass of profit will grow even if the rate of profit does not. The result is a tetra society of four classes: a surplus population kept quiescent by transfers and cheap entertainment, a precarious service-sector working class, a homoploutic elite combining high labor and capital incomes, and a small stratum of techno-lords. Such a society would lack a middle class in the twentieth-century sense, and richer, more AI-intensive societies could therefore prove more politically unstable than poorer ones.