Samsung, once known for infrequent (if not nonexistent) updates to its handsets, has changed tactics with its 2015 releases, with most of its current phones receive semi-regular updates. We don’t know what’s in most of them, but presumably its bug fixes, security improvements and the like.
Anyhow, rumour has it Samsung is working in a significantly more major update for a number of its 2015 phones, including the Galaxy S6, S6 Edge (and Edge+) and the Note 5. There’s speculation that it could be the Android 6.0 Marshmallow update, but I don’t think so; the final code hasn’t even been released yet, so Samsung working on a release yet just doesn’t quite gel. More likely, the update is focused at bringing increased stability to Android 5.1.1, and new features to the Note 5 and S6 Edge+.
SamMobile reports that the firmware version for the S6 Edge (for example) will jump from G925FXXU2COH2 to G925FXXU3COI6, with the change from U2 to U3 usually indicative of major user-facing changes. They’re fairly confident that its a Marshmallow update, but with no other manufacturers reportedly working on it yet, and with Google not having even released the OS yet, it does seem unlikely.
Of course, when and if we find out, we’ll be the first to let you know.