The issue with the upgrade of Android to Version 6.0 (also known as Android M or Marshmallow), is that even though it officially rolled out last October, that doesn't mean that it is on every new Android device.  The good news for users of newer Android devices is that it is starting to slowly spill out, and Samsung, who is one great champion of Android devices, is starting to get it.  This is what is known about the Android M Version 6.0 Marshmallow Release Date for Samsung Galaxy S6, S6 Edge+, Note 5, Note 4, Note Edge, and S5 on US Cellular, T-Mobile, Verizon, AT&T, and Sprint.

A report from Gotta Be Mobile states that the rollout began with an Android M Beta test in Korea, and this allows certain users to receive the upgrade early.  For example, the Galaxy Note 5 owners got version 6.0, and some users of the Galaxy S6 are getting  Marshmallow as well. 

The most recent and good news for Galaxy S6 users is that Samsung stated that the update for the S6 will begin this week.  Considering that the S6 is the flagship phone unveiled last year, it makes sense that they would get it first, along with the S6 Edge.  One would think the some of the other recently released Android devices, such as the Galaxy S6 Edge + and the Note 5 would get it about at the same time.  One estimation has been late February or early March, at least for those models. 

Other Samsung devices that are due to get the update include the Galaxy S5, Galaxy Alpha, Galaxy A7, Galaxy A8, Galaxy Note 4, Galaxy Edge, Galaxy Tab S2, and possibly the Note 4 Edge.  Pocket Lint reports that the S5, Note 4, and Note Edge should get the upgrade sometime between March and April.  As for the others, it could be somewhere within Q1 or Q2 of 2016, with nothing more specific than that. 

Tech Radar reports that the Galaxy S6 and the S6 Edge are both getting the Marshmallow update now, but it has taken quite a bit of time to get here plus it will depend on the model and carrier of your device as far as when you will actually get it.  Considering that Android rollouts often come to some carriers like US Cellular, AT&T, T-Mobile, Sprint, and Verizon first before coming to the same others. 

In other words, if you have a Galaxy S6 device, including the Edge, it is highly recommended that you go to your "Settings" menu to see if you can download an OTA (Over The Air) update of Android M.  The Verge says that this update has been available as of February 15^th.  If you have an older Samsung device, then you should continually check it as well until you can get that download.