Google introduced seamless updates back in 2016 with Android 7.0. Any Android smartphone that features Seamless System updates will have two partitions; A and B and when a firmware update arrives, it is downloaded and installed on the second inactive partition. Once the update is downloaded and installed, the phone will boot into the newly updated firmware.
The key motive behind this feature is user can continue using the phone during an OTA (over-the-air) update installation process with very little downtime. Moreover, it also reduces the risk of errors on a new OTA firmware and if something does happen during the update process, the phone will boot into the old partition, until the new update is tried again.
After Google, LG, HTC, Motorola, OnePlus, ASUS, Sony and others introduced seamless updates, but Samsung, OPPO, HUAWEI and Vivo still don’t use this so updates are done through a dedicated updater in a recovery process making the users wait for several minutes before it is complete.
Google won’t allow this from Android 11 so all the Android 11 devices will have to support seamless updates in devices launching later this year or early next year. This is confirmed by the latest commit to the AOSP Gerrit titled “Require Virtual A/B on R launches.” by a software engineer at Google on the Project Treble team.
The commit updates the Vendor Test Suite (VTS), which is an automated test that all the devices must pass to be considered compatible with Project Treble. This will check if a device launching with Android 11 or higher supports virtual A/B partitions. If the device fails VTS, then it cannot ship with Google Mobile Services. So it is compulsory for all OEMs using Google Services to have virtual A/B partitions and seamless updates.