Apparently there was a major update to Stockfish recently such that it gained +50 elo (per regression tests). I'm told that the difference is coming from the new NNUE (efficiently updatable neural network) eval function. In other words Stockfish is now a hybrid engine utilizing AB search & NN eval.
- Is this picture correct?
- If so, how is the NNUE being trained? Is it only being trained on Stockfish games, or does it also utilize games by other engines?
- If NNUE is being trained on Stockfish games, does that mean Stockfish's original handwritten eval will continue to be tested and improved on? Or will Stockfish NNUE be trained on Stockfish NNUE games in the future (i.e. the handwritten eval is now obsolete and will not be developed anymore)?
- Does this mean Stockfish's update process will now take longer? In the sense that for every new patch, a new NNUE would need to be trained, and then the new patch + new network plays against the old patch + old network?