The Samsung Galaxy A8 from last year was preinstalled with Android 5.1 Lollipop. However, recent leaks indicate the device will get Marshmallow rolling out soon.
The dual-SIM variant of the device was spotted having a Wi-Fi Certification, which mentions the A8 was running Android 6.0.
We should consider this info as not official, but it is almost certain that the A8 will receive the newest update sometime in the future.