All PHB classes and their subclasses will be available on release (only certain ones will be available during early access). They've said their base is PHB/MM/DMG but with Githyanki showing it means they can pull from other sources as needed.
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After reading all the Q&A I don't know how any BG1/2 fans can still be fearful, unless it's already been decided in their minds they'll dislike the game.