Today we published our paper on beating the human state of the art in Gocache, the only major board game where humans (or at least top professionals) could still beat computers. No more. Our program AlphaGo achieved a 99% winning rate against the strongest existing Go programs, and defeated the human European champion by 5 games to 0.
(That's me playing at 0:10)
The first major breakthrough in computer Go - after remaining at weak amateur level for decades - came with the advent of Monte Carlo Tree Searchcache (MCTS) around 2007, massively improving playing strength. Still, Go programs remained much weaker than strong human players and started to plateau again fairly soon - Crazy Stone's feat of defeating a professional player with 4 (!) handicap stones in 2013 remained unsurpassed since 2013.
There are many reasons Go is difficult for computers - a huge state space (10^171 vs ...