More precisely, the first device that will have the honor will be the Galaxy A5. The device was produced back in 2014, and there are many customers who already are hyped for this release.
The Australian carrier, Optus, has confirmed that Nougat is already testing for the Galaxy A5 devices. they also announced that if everything goes fine with the testing, they will roll out the update in late January.
Officially, back in 2014, the Galaxy A5 was launched with the Android 4.4 KitKat. Since then he got timely updated with the newer versions, the Marshmallow and the Lollipop. And now, if it happens to have the Nougat version, the Galaxy A5 will become the first device to be longest-supported Samsung smartphone ever.
For now, nothing is yet confirmed officially from Samsung, but what we can expect is to release the update either in late January or some months after that, and hopefully it will be available worldwide.