Historical Rules · 23 August 2019
Rule 902.5b
Official source text from the 23 August 2019 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 their cleanup step begins, they will discard all but six of them.