Samsung is the biggest Android smartphone manufacturer, but it is not known for rolling out software updates to its devices fast. The reason behind the delay is usually optimising Google's new firmware with Samsung's own TouchWiz UI, staged roll-out and device eligibility.

Samsung is currently running a beta test programme for Android 6.0 Marshmallow on Galaxy S6 and S6 Edge devices in South Korea and the UK.

But, it appears like Samsung might have slipped a beta version of Android 6.0.1 Marshmallow to a lucky Galaxy S5 owner. The unreleased software arrived over-the-air, but looks like an error on Samsung's end, SamMobile reported.

As Android Authority pointed out, the Android 6.0.1 Marshmallow running on Galaxy S5 isn't a final build. In fact, the final firmware is expected to come with a new and updated TouchWiz. In one of the screenshots shared by SamMobile, the Android security patch version is listed as "1 January 2016," which is an indication that the leaked firmware isn't final or official.

It is certain that Samsung's current and former flagship devices will be updated to Google's latest firmware, but do not expect it soon.

The official beta testing programme involving Galaxy S6 and S6 Edge smartphones concludes on 18 January, which means the Android 6.0 Marshmallow can be expected only after that. Moreover, the Android 6.0.1 Marshmallow roll-out status is completely unknown at the moment.