Of all the major science fiction TV series currently running, Foundation is somewhat unique insofar as its timeline is incredibly vast. While Apple TV+’s , which was the third book in Isaac Asimov’s original Foundation trilogy. Season 3 adapted much of the second half of the novel Foundation and Empire.
However, the revelation that there are hidden robots hanging out near Earth, also is a nod to the much later Asimov novel Foundation and Earth, so Season 4 could pull from two books at the same time.
It’s also possible that like much of the series, Foundation Season 4 will strike out in an entirely new and original direction.