The much anticipated migration of all accounts to global, also known as single-user login finalization, is happening next week. The renaming is scheduled to begin on Wednesday, 15 April, and is expected to last about a week, although realistically it could take anywhere from three days to two weeks. We shall see.
2.8 million accounts were contacted on their talk pages about impeding renaming over three weeks ago, and if email was confirmed they received an email notification as well. Since then ~1.34 million accounts have either merged and attached or been renamed.
~1.46 million accounts will be renamed next week. They will still be able to log in with old credentials, which will then provide information about the account renaming. All accounts will also receive a talk page notice about the renaming, and invite them to request a new name if they choose. Please help translate this into your language if it's not done so yet: https://meta.wikimedia.org/wiki/Single_User_Login_finalisation_announcement/Post-rename_notice