Even though the Samsung Galaxy S5 isn't scheduled to receive Android 6.0/Marshmallow until sometime in April, we have a report that a lucky owner was accidentally sent the update via OTA push. Interestingly, according to this report, this is actually the second time we have seen that happen over the past couple of months.
We can't fathom why a mistake like this could/would be made, but the user reports that it is stable and working fine, so he/she has reason to celebrate. What's especially reassuring about this is that Samsung is obviously ahead of schedule for the development of the Marshmallow update (at least as far as the Galaxy S5 is concerned).
Here's our dedicated Samsung Galaxy S5 section for further discussion: Samsung Galaxy S5 Discussions
Source: Frandroid