Samsung has updated the Security Updates page on its website. While some 2016 models -including Galaxy J1 (2016), J3 (2016), A3 (2016) - have been removed altogether, what's surprising is the recently launched Galaxy A8+ (2018) is in the 'quarterly security updates' section. This means the device won't get monthly updates. The Galaxy A8 (2018), on the other hand, sits in the 'monthly security updates' section. As for other changes, the Galaxy J2 (2018) and the Galaxy Tab Active 2 both have been added to the quarterly list. The Galaxy S9/S9+ flagships haven't yet made it to the list...
Source: https://www.gsmarena.com/samsung_galaxy_a8_2018_to_only_get_quarterly_security_updates-news-29946.php
