Charlotte F. answered 10/07/19
Cambridge English Graduate Available to Tutor English Literature
As you rightly note, both Endymion and Hyperion are based on Greek mythology. In that respect, they are certainly related, and there are arguments to be made about their relationship on the basis of that. They are separate projects, however. Hyperion has two versions, showing Keats was probably intending to expand it further. The stories are also rather different. Endymion focuses on a forbidden/doomed love whereas Hyperion engages rather more with epic themes.