According to industry observer SamMobile, an insider source has confirmed that Samsung has already begun testing the new Marshmallow upgrade on some of their devices, with recent flagship releases topping the update list.

According to the website, the phones included on the list for the upcoming Android 6.0 Marshmallow update are the recent flagships in the Galaxy series, namely the Galaxy Note 5, Galaxy Note 4, and Galaxy S5. In addition, also included is the mid-ranged Galaxy S5 variant, Neo.

The website also has a complete list of purported Samsung devices making the jump into Android 6.0 Marshmallow, with some of the listed smartphones carried by major mobile carriers. If the list proves true, then it would be confirmed that there will indeed be an over-the-air update for most Samsung devices.

Meanwhile, another industry observer, GottaBeMobile, reported that even if Samsung is still silent about what devices will be included for the Android 6.0 update, T-Mobile has already included the newer flagships Galaxy S6, Galaxy S6 Edge, and Galaxy S6 Edge+ on their list of targeted device updates. The mobile carrier listed the three flagships to be under "manufacturer development phase," which means that there will be confirmed updates for these devices.

However, although Samsung-centric websites like SamMobile claim that details are from an insider source, Samsung has yet to confirm if the speculations and rumors are true and come out with a statement for a specific release window for the Android 6.0 Marshmallow update.