Powerful AI will change our institutions. Yet most of our attention is on aligning or regulating AI, while treating our institutions as fixed. Introducing Pax Machina: a new publication about the institutions we need for powerful AI. It is edited by @MaxKronerDale, @sebkrier, @NoemiDreksler, @LiamPatell, @chelcott9, @synchroaphasia, @ryan_t_lowe, @edelwax, and @klingefjord. The editorial board consists of Peter Railton, @sethlazar, @saffronhuang, @AmmannNora, @xuanalogue, @IasonGabriel, @hamandcheese, and @deanwball. Our goal is to seed rigorous debate about what a world of humans and powerful AI could and should look like. We will publish proposals for new institutions, counterproposals, well-justified design principles, and analyses that change how a class of institutions should be designed.