How Much Do the Pros Actually Play a "Game Theory Optimal" Style?

"Game Theory Optimal" — or "GTO" — is a term often heard in poker these days. Often the term is used imprecisely as a general reference to the "best" style or strategy in a given situation, though in truth it has a much more specific meaning than that.

To employ a "GTO" style means to play in a way that is impossible to be exploited by an opponent. It means always making "optimal" decisions that ensure you maximize your expected value in any situation. To play such a style perfectly would also mean that the very best your opponent could do against you would be to break even.

Such a style can be readily employed in simple games, but in more complicated ones like no-limit hold'em it is hard…