By now, the rollout Android 6.0 Marshmallow, or Android M, to Google's own Nexus line of devices is about to begin. Motorola and HTC have announced, which devices are first slated for the upgrade as well.

And now Samsung, while remaining officially mum on their rollout process, is now rumored to be preparing for a "major update" for its top devices, according to insiders who hinted it could be Android M to SamMobile.

The four 2015 flagship devices -- Samsung Galaxy S6, Samsung Galaxy S6 edge, Samsung Galaxy S6 edge+ and the Samsung Galaxy Note 5 -- are all on the list for which the Korean device manufacturer is "currently preparing a major update," as the SamMobile put it based on its unnamed sources.

The site further emphasized that their sources noted this next update for the four 2015 Samsung flagships would be "bigger than the usual updates" occasionally rolled out to flatten bugs.

The other possibility is that this upcoming "major update" would just be a more stable version of Android 5.1.1, especially for the Samsung Galaxy S6 and Galaxy S6 edge.

But given those four particular phones slated for the update, an Android 6.0 Marshmallow OTA rollout is not out of the realm of possibility, especially as other Android OEMs like HTC are preparing to debut a new smartphone running Android M right out of the box as early as mid-October.

HTC's upcoming Marshmallow phone, plus the painfully slow rollout of Android Lollipop last year, may hint that Google is offering OEMs more access and support to get the ball rolling faster this time around.

Android 6.0 Marshmallow comes with several improvements and new features, including the battery saving "Doze" mode, more control over app permissions, built-in fingerprint scanner support, and the latest most intelligent AI assistance with Google Now on Tap.