Thank you Quinn for the quick answer. It is also very thoughtful to give the definitions of the terms, really helpful to me. Reading your post and the referenced one, my app does not manage keychain items such as user's passwd, so the loss of keychain items is not an issue for me, I conclude the best approach for me is to follow your recommendation "publish the app with the new prefix. That’s a good idea in general". If I publish the update (new version) of my app with newer App ID Prefix while keeping the same bundle ID, will my current customers be able to install the update fo free as the same app that they already payed for? In other words, will iPhone considers that they are the same app despite the difference in APP ID Prefix (but always with same bundle ID) ?