Machines have topped the best humans at most games held up as measures of human intellect, including chess, Scrabble, Othello, even Jeopardy!. But with Go—a 2,500-year-old game that's exponentially more complex than chess—human grandmasters have maintained an edge over even the most agile computing systems. Earlier this month, top AI experts outside of Google questioned whether a breakthrough could occur anytime soon, and as recently as last year, many believed another decade would pass before a machine could beat the top humans.

But Google has done just that. "It happened faster than I thought," says Rémi Coulom, the French researcher behind what was previously the world's top artificially intelligent Go player.

Researchers at DeepMind—a self-professed "Apollo program for AI" that Google acquired in 2014—staged this machine-versus-man contest in October, at the company's offices in London. The DeepMind system, dubbed AlphaGo, matched its artificial wits against Fan Hui, Europe's reigning Go champion, and the AI system went undefeated in five games witnessed by an editor from the journal Nature and an arbiter representing the British Go Federation. "It was one of the most exciting moments in my career, both as a researcher and as an editor," the Nature editor, Dr. Tanguy Chouard, said during a conference call with reporters on Tuesday.