As of January 1st, 2025, Romania and Bulgaria will officially become full-time members of the Schengen Area. Both countries have been members of the European Union (EU) since 2007, but as they were not part of the border-free area, travelers were still required to show passports upon entry.
By joining the Schengen Zone, travelers arriving by air or sea from other Schengen countries will no longer have to show passports upon arrival. They will maintain checks at land borders between Hungary and Romania and between Romania and Bulgaria for "at least" six months to "prevent any serious threat to public policy and internal security." This means if you are driving or arriving by train or bus into Romania and Bulgaria, you will still need to carry your passport.
More information about the application can be found here.