As of now, the Samsung Galaxy S8 and the samsung Galaxy S8+ will only receive quarterly updates. This means that instead of getting a new security patch every month for the updates to be bundled together and released at the end of three months.
In the S8 the duo’s three-year-old, who was released in April of 2017. Initially it ran Android, To 7.0, and Nougat, and it has since been updated to Android, For 9 Cake with An ONION (in the original). Android, the 10 update is not coming.
By way of comparison, the Samsung ended support for it in 2016 samsung Galaxy S7 duo has in the last month, after a two-year-long, monthly updates, and in the quarterly schedule. Samsung originally wanted to end support for the S7-phones, a year ago, but abandoned it and went on releasing updates for about 10 months.
This way, you can expect that your samsung Galaxy S8 or S8+ will be supported until at least 2021.