Cirroc Lofton reprised his role as Jake Sisko! In the form of a recording of a lecture he gave, and as... not sure, but the simplest explanation would be a figment of Sams imagination.

Tawny Newsome is back, playing an instructor. Who is a joined Trill... Illia Dax. Yes, that Dax. Has ridges sort of like the Trill in TNG, though it's unstated if Illia is from that Trill variant or if Dax was put into a non-Trill after the experience with Adira Tal showed it to be possible.

And while he didn't come out of retirement to do it, Avery Brooks gave permission to use an excerpt from a spoken word piece on one of his jazz albums.

I'd seen some reports that this episode was also a followup to City on the Edge of Forever, but except for an image on a monitor in the background of the Guardian in portal form, there was nothing to link the two episodes. I wonder if it's actually a future episode that will follow up, or if someone saw that image and made some unjustified assumptions?