The nine classes and the playable races of World of Warcraft: Forever, with their icons. Each class links to its talent calculator.
The game client contains nine classes: Druid, Hunter, Mage, Paladin, Priest, Rogue, Shaman, Warlock and Warrior (game client data, matched by the Warcraft Wiki). Class talents are rebalanced so that more choices are viable (Warcraft Wiki).
No official source details the classes one by one, so we are not writing specialization guides at this stage. The talent calculator, however, shows each class's real trees, read from the client data.
The game client lists the eight original WoW races and the Skyborne, the new race announced by Blizzard that comes with the Skyborne packs. The Skyborne exist in two versions, one per faction.
The faction and full name of the two Skyborne versions come from the game client data (build 1.60.1.69913), not from a Blizzard announcement: they may change with patches.
Wikipedia cites Forsaken Paladins and Dwarf Shamans, two combinations absent from the original game. The Warcraft Wiki lists more, but its list mixes in combinations already present in WoW Classic, so we are not repeating it until it is confirmed.