In more detail, the dealer will peek at their face-down card (hole card) when their upcard is either an Ace or a ten-value card (10, Jack, Queen, King). If the dealer has a blackjack, the hand is immediately resolved without further action from the players, preventing them from making unnecessary decisions like hitting or doubling down.
Dealer Peek Example
For example, if the dealer’s upcard is an Ace, they will peek at their hole card to see if they have a ten-value card, resulting in an automatic blackjack if present.