DeepMind's Go-playing program, which beat world champion Lee Sedol in 2016. Its unexpected 'move 37' became a touchstone for machine creativity.
At the time that the book came out in 2016, a lot of people viewed deep reinforcement learning as the culmination and questioned the fact that we weren't covering how AlphaGo worked in detail; many viewed AlphaGo as the culmination of AI at the time.
Ian Goodfellow, Ian Goodfellow on Inventing GANs
Go at the time was the game that even the AIs weren't close to the human champions. Then not that much later we got AlphaGo and saw that just completely crumble.
Dmitri Cherniak, Dmitri Cherniak on Strictly for Art