Larian Studios Forums Baldur's Gate III Baldur's Gate III - General According to Sir Tolkien, a party size is 6.

Come to think of it, the other major game I could see where 4 is a minimum is probably Shadowrun and mostly for the same reasons as D&D: it's a game that heavily favors characters being built toward specialty roles rather than self-sufficiency. You need a decker, a magic person, a sammie, and a face. You could probably go down to 3 and spread some responsibility, but 2 leaves too many holes. Same with D&D, you need support, utility, damage, and tank, and you can maybe go down to 3 and spread one of those roles out, but at 2 things become inconvenient.

Edit: I have been asked to point out that the Monster Manual says flat out that all Challenge Ratings are based on a party size of 4 characters.