An Interesting Bishop Endgame (Real Game Tactics 22)

This game was recently played at the Lev Gutman 70th Birthday Jubilee Tournament between GM Aleksandr Karpatchev and IM Thorben Koop. The end of this game was an interesting same colored bishop endgame.

White to move, which move needs white to win? There are more moves that are winning, but after a few moves you also have to play this move.