As of August 6, the efficiently updatable neural network (NNUE) evaluation has landed in the Stockfish repo! What is NNUE? Both the NNUE and the classical evaluations are available, and can be used to assign a value to a position that is later used in alpha-beta (PVS) search to find the best move. The classical evaluation computes this value as a function of various chess concepts, handcrafted by experts, tested and tuned using fishtest.
