They make statements on the long-run average lift, which is a quantity that many businesses care about: what will my average lift be if I implement a variation

They make statements on the long-run average lift, which is a quantity that many businesses care about: what will my average lift be if I implement a variation after my A/B test? Could you state clearly what this guarantee is? Unless I'm making a stupid mistake, such guarantees are impossible even in principle with frequentist statistics.