From the introduction: The Masters campaign is intended for those invested players with some experience with the D&D Adventurers League. As such, you can join with the Masters campaign with any Seasonal or Historic campaign D&D Adventurers League character that has reached 5th-level. A character that has migrated from the Seasonal campaign to the Historic campaign may not later choose to migrate to the Masters campaign. Once a character has chosen to migrate to the Masters campaign, they may no longer participate in Seasonal or Historic campaign adventures.