Historical Rules · 17 July 2015
Rule 902.5b
Official source text from the 17 July 2015 Rules release
A player’s maximum hand size is seven, as modified by the hand modifier of his or her vanguard card. Example: The hand modifier of a player’s vanguard card is -1. That player’s maximum hand size is six. If that player has more than six cards in his or her hand as the cleanup step begins, he or she will discard all but six of them.