The Samsung Galaxy S8+ is already receiving its first software update. The release comes despite the fact that it's not even officially available everywhere yet. So unless you already have an S8+ in hand, when you get yours this update should be waiting for you once you power the device on for the first time.
Currently, the update is rolling out in Europe. It's been spotted in Belgium and Germany so far, and will undoubtedly make its way to other markets in due course. As always with over-the-air updates, it may take a while for it to reach all units. Also keep in mind that if you purchase a carrier-specific version, you could be in for an even longer wait.
After you apply the update, your Galaxy S8+ will be on build NRD90M.G955FXXU1AQDD, at least in Europe. The new software brings with it the latest security updates, and after you install it you'll have the April 1, 2017 security patch level. That's it - no new features this early in the game.
I just updated and can no longer remap Bixby. It worked before the patch :(
Just got it on my S8. It's 664.21MB and in the change log, in addition to the usual bug fixes part, it states the stabilisation of new functions such as DeX and Bixby and stabilisation of face recognition algorithm.
Just got it for my S8 on tmobile, it was indeed the April security patch