96 bits is not nearly enough, as there are ~4.8 * 10^44 > 2^148 legal chess positions (with side to move/castling/ep info) [1]. Chess Position Ranking provides

96 bits is not nearly enough, as there are ~4.8 * 10^44 > 2^148 legal chess positions (with side to move/castling/ep info) [1]. Chess Position Ranking provides a 153 bit encoding but it's very slow to decode. If the encoding only needs to work for the set of positions occurring in some database, then there's almost no limit to the number of coding optimizations one can make (until the encoding just becomes an index in the set of all unique db positions). [1] https://github.com/tromp/ChessPositionRanking https://github.com/tromp/ChessPositionRanking