Samsung is a huge brand and therefore, it’s not possible for them to push updates to every device superfast due to the number of different devices it has created (And is still creating!). However, there is some good news for Galaxy S6 AT&T users, Samsung has stated that the device is going to be next in the line to get the Marshmallow upgrade after already updating most of the other carrier variants.
The update will carry the software version G920AUCU3CPC2 and thanks to the Marshmallow-ey goodness, users will be able to see a good number of improvements. Samsung’s support website has this news but there is no official information regarding this on AT&T’s website.
Anyway, you are welcome to destroy the update button on your device, it can be found here: Settings>System>About device>Software update>Check for updates.
Main image credit: CNET