Two of the casting classes we’ve seen were previously “spells known” casters, but are “prepared” casters in the UA, so it seems likely that they are considering switching all casters to be “prepared” casters. Additionally, instead of preparing a number of spells of any level equal to your level (or half your level for half-casters) plus the relevant casting ability modifier, you instead prepare a number of spells of each level equal to the number of spell slots you have of that level. So, for example, a 5th level bard always prepares 4 first level spells, 3 second level spells, and 2 third level spells. Additionally, so far we have not seen individual class spell lists. Clerics prepare spells from the Divine spell list, Bards prepare Divination, Enchantment, Illusion, and Transmutation spells from the Arcane spell list, and Rangers prepare non-Evocation spells from the Primal spell list. Cleric and Bard also each got a short list of spells that are always prepared for them (bards, for example, got lots of always-prepared healing spells, since healing is a bard thing I guess, and the Arcane spell list doesn’t have any of those).