But in a world of advanced robotics and AI, this correction mechanism will break. That is, though Piketty was wrong about the past, he will probably be right about the future.

Indeed, in some ways, he may well be more right than he knew. A lot of AI wealth is being generated in private markets, which only large and sophisticated investors have access to. You can’t get direct exposure to xAI from your 401k, but the sultan of Oman can. This trend toward the “privatization of returns”, already ongoing (1, 2, 3) and especially pronounced in the AI startup world, could well continue indefinitely.

Furthermore, with full automation, the main source of catch-up growth for developing countries goes away; namely, that by importing capital and know-how, they rapidly make their underutilized labor more productive.

If AI is used to lock in a more stable world, or at least one in which ancestors can more fully control the wealth they leave to their descendants (let alone one in which they never die), the clock-resetting shocks could disappear. Assuming the rich do not become unprecedentedly philanthropic, a global and highly progressive tax on capital (or at least capital income) will then indeed be essentially the only way to prevent inequality from growing extreme. Without one, once AI renders capital a true substitute for labor, approximately everything will eventually belong to those who are wealthiest when the transition occurs, or their heirs. Or more precisely, it will belong to the subset of this group who save most and most invest with a view to maximizing long-run returns.