Libratus is playing thousands of games of heads-up, or two-player, no-limit Texas hold’em against several expert professional poker players. Now a little more than halfway through the 20-day contest, Libratus is up by almost $800,000 against its human opponents. So victory, while far from guaranteed, may well be in the cards.
A win for Libratus would be a huge achievement in artificial intelligence. Poker requires reasoning and intelligence that has proven difficult for machines to imitate. It is fundamentally different from checkers, chess, or Go, because an opponent’s hand remains hidden from view during play. In games of “imperfect information,” it is enormously complicated to figure out the ideal strategy given every possible approach your opponent may be taking. And no-limit Texas hold’em is especially challenging because an opponent could essentially bet any amount.
“Poker has been one of the hardest games for AI to crack,” says Andrew Ng, chief scientist at Baidu. “There is no single optimal move, but instead an AI player has to randomize its actions so as to make opponents uncertain when it is bluffing.”
Libratus was created by Tuomas Sandholm, a professor in the computer science department at CMU, and his graduate student Noam Brown. Sandholm, an expert on game theory and AI who emigrated from Finland for his PhD, says it is amazing that humans have been able to outplay computers for so long. “It just blows my mind how good these top pros are," he says. "Of all of these games that AI has tackled, [poker] is the only one where AI hasn't reached superhuman performance.”
AI researchers use game theory, or the mathematics of strategic decision making, to find the best strategy given various uncertainties, known as an equilibrium. Because the possibilities are so vast, this usually involves some form of approximation.
