The primary factor is whether or not the flight is CPU eligible. If it’s a CPU eligible flight (domestic or international) any premier member is able to confirm into PN instantly on a Y or B fare, and M fare if 1K or GS.

If it’s a non CPU route (long haul domestic or international) instant upgrades are not available and a 1K GPU will need to clear into PZ. With an M fare, you would clear before any other 1K’s on lower fares.