The Ke Jie vs. AlphaGo games quickly reached a position that was not in the GoGoD game collection of almost 90,000 professional game records: Game 1 was unique at move 5, game 2 was unique at move 7. To me, this seemed very early, and @badukaire on Twitter got me to wonder: How soon does a pro game usually reach a position that’s different from any previously played game?
Time for some data: I ran SmartGo’s fuseki matching on the whole GoGoD game collection (excluding handicap games). In that data set, the highest probability for a move to become unique is at move 8; the median is between move 11 and 12; the average is about move 13. Games are unique by move 7 in about 16% of games; by move 5 in only about 4%.
So it’s somewhat unusual to diverge from standard play that early, but there’s more variety of play early in the game than I expected. Also, I’m sure that a lot of games will soon be copying those moves by AlphaGo and Ke Jie, and those opening moves will be unique no more.