Alpha Zero Chess never made their code or models public. Leela is based on the same ideas as Alpha Zero Chess, but its model and code are public and uses crowd

Alpha Zero Chess never made their code or models public. Leela is based on the same ideas as Alpha Zero Chess, but its model and code are public and uses crowd sourcing to generate and refine the model. Stockfish uses a combination of classic Alpha-Beta pruning along with a type of AI called NNUE to evaluate positions.