I'm assuming a sudden death if still tied??
U.S. Open playoff format
If a playoff were to be needed at Pinehurst, it would be a first for the U.S. Open since 2008. That summer, Tiger Woods bested Rocco Mediate in a Monday playoff after the two finished tied after 72 holes. Back then, the USGA still used an 18-hole playoff format. Nowadays, they make things a little more simple.
Since 2018, the USGA has implemented a two-hole aggregate playoff format in the event of a tie after 72 holes, ensuring a champion would be crowned by Sunday evening.
edited to say...never mind.....🤣