The new API will give developers the choice of letting an app lock users out while it installs updates or to let users continue using them as the update is downloaded and installed in the background. The former doesn’t boot you out per se, but the update window takes up the entire screen, so you’re essentially prevented from using the app while the update occurs. According to the example provided by Google, the first one – called “immediate in-app update” – will also have an on-screen pop up, letting you know that an update is available. This, and the fact that you’re now allowed to use the app until the update is complete, suggests that this method will be used for critical updates like bug fixes and security hole plugs.
The latter – which Google calls “flexible in-app update” – will be for new but not pressing features. We think so simply because it looks like you have to actively seek out the update, instead of having a pop up appear on your screen. The announcement was made during the Android Developer Summit, where support for foldable displays was also made. From the looks of it, it’ll be awhile before app devs get access to this API, and even longer before we actually see it in any app. (Source: Google)