If the update in partition B fails to boot or is buggy, the system automatically reverts to partition A. This prevents the device from becoming "bricked" during a failed update process.
These packages often contain only "differential" data, meaning the file size is much smaller because it only includes what has changed since the last version rather than the entire operating system.
The system maintains two separate partitions (A and B). While you are using partition A, the AB-GOTA.zip file installs the new update to partition B in the background. You only experience a brief restart to switch to the new version.
Are you trying to this update on a specific device, or A/B (seamless) system updates - Android Open Source Project
Modern "Virtual A/B" updates (common in Android 11+) use compressed snapshots. Instead of needing double the physical storage, the AB-GOTA.zip package only writes the differences (diffs) to the storage, significantly reducing the disk space required for the update.
The most interesting feature regarding this file format is its capability: