Historical Rules · 17 June 2011
Rule 407.2
Official source text from the 17 June 2011 Rules release
When playing for ante, each player puts one random card from his or her deck into the ante zone after determining which player goes first but before players draw any cards. Cards in the ante zone may be examined by any player at any time. At the end of the game, the winner becomes the owner of all the cards in the ante zone.