A Facebook spokesperson confirmed to Mashable that some users began to notice the change Wednesday — but that it is not yet affecting all of Facebook's mobile users.

The change will only affect users of the iPhone and Android app; messages will remain in the iPad and Windows Phone app. It's not clearly exactly how long it will take for all of Messenger's holdouts to see the change, but the spokesperson said it will continue to roll out over the coming weeks. Although the main Facebook app has been prompting users to download Messenger since April, when the company announced it would be making the switch, users could still access messages without downloading Messenger until now.

Facebook has been slowly ramping up to this change since the spring, when Facebook first announced it would be requiring mobile users to download both apps. Last week, Messenger holdouts received an email alerting them their messages would be moved over to the Messenger app in the very near future. Though some users remain unhappy about the move, Facebook has maintained switching to Messenger will benefit all users as messaging with Messenger is faster and more reliable. The app, which first launched in 2011, already has more than 200 million monthly users, the company reports.