Historical Rules · 27 April 2018
Rule 902.5b
Official source text from the 27 April 2018 Rules release
A player’s maximum hand size is seven, as modified by the hand modifier of their 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 their hand as the cleanup step begins, they will discard all but six of them.