Does the second player on the first turn have to draw a turn or do they start with 4?

In a 1v1 game of Riftbound, both players start with 4 cards in their opening hand. Regarding the first turn:

Yes, the second player draws a card on their first turn.

According to the standard turn sequence and RiftJudge FAQs (such as FAQ #2709 and #6298), players do not draw simultaneously. Instead, each player draws a card during the Draw Phase of their own turn.

The sequence for the start of the game is as follows:

1. Opening Hand: Both players draw 4 cards and may perform a mulligan.
2. Player A's First Turn: Player A channels 2 runes and draws 1 card during their Draw Phase.
3. Player B's First Turn: After Player A's turn ends, Player B begins their turn. Player B channels 3 runes (an extra rune as compensation for going second) and draws 1 card during their Draw Phase.

As noted in RiftJudge FAQ #6381, the rule where a player does not draw on their first turn only applies to specific multiplayer formats (such as FFA 3, FFA 4, and 2v2 Magma Chamber) and does not apply to standard 1v1 games.