Artificial intelligence has made history by beating humans in poker for the first time, the last remaining game in which humans had managed to maintain the upper hand.

Libratus, an AI built by Carnegie Mellon University (CMU), racked up over $1.7 million worth of chips against four of the top professional poker players in the world during a 20-day marathon poker tournament that ended Tuesday in Philadelphia.

While machines have beaten humans over the last two decade in chess, checkers, and most recently in the ancient game of go, Libratus' victory is significant because poker is a game of imperfect information — similar to the real world, where not all problems are laid out and the difficulty in figuring out human behavior is one of the main reasons why it was considered immune to machines.