Mishaal Rahman: Google is preparing to fully remove support for non-A/B updates from Android, leaving A/B updates as the only officially supported OTA update mechanism moving forward.
Mishaal Rahman: Google is preparing to fully remove support for non-A/B updates from Android, leaving A/B updates as the only officially supported OTA update mechanism moving forward.

Mishaal Rahman (@MishaalRahman@androiddev.social)

Not just seamless, but safer updates as well. A failed boot from the newly updated partition(s) can be detected with the malfunctioning slot flagged by the lower-level bootloader, allowing for an instantaneous rollback.
This could break devices that are older
How many devices are that old but still getting updates?
My 6 year old OP6 has A/B partitions.
Older devices wont break unless you force install without creating the necessary filesystem partition layout first. Depending on how you define older that might only be a small hurdle. If you define it as a device designed for Android 4 you're likely gonna have a bad time.