Neo's back in the Matrix and not-so-blissfully unaware of what has (or will?) transpire, but evidently soon makes connections. Most of the old cast is back, with Neil Patrick Harris a prominent newcomer, and Yahya Abdul-Mateen II as Morpheus.
Lawrence Fishburne says that he wasn't asked and hasn't been told, though it also seems likely that there is some cleverness at hand in the gnostic tradition of the series (e.g. the sly suggestion it is a prequel, not a sequel—or perhaps some sort of multiversal knot as is currently fashionable)