How is upwards mobility maintained in an age where real AGI is achieved?

This is a question I have been thinking about but can't determine an answer to. If the goals of AI are legitimately realized -- the elimination of human cognition as a valuable labor input and the eventual replacement of all human tasks with machines -- then how would upwards mobility be maintained? While it is difficult to make predictions of the impact this would have the economy (besides noting that it would be drastic) I find that most optimistic post ai solutions involve some sort of ubi.