Are you having some major issues with your iPhone 6 Plus? The good news is that according to MacRumors, it seems that Apple will be replacing some iPhone 6 Plus units with the iPhone 6s Plus, which means that for some users, you will essentially be getting a free upgrade of sorts, even if that upgrade is about 3 years old.
The reason for this upgrade? It is unclear why as Apple did not state the reason, but it has been speculated that the reason could be due to the fact that iPhone 6 Plus batteries are difficult to get, which means that repairing the iPhone 6 Plus could add delays, so replacing it with the iPhone 6s Plus might be a more efficient route.
However the bad news is that it looks like only devices that are eligible for whole-device repairs will get the replacements, and even then Apple does not specify which iPhone 6 Plus units are eligible either. This means that it could really depend on your luck, as well as the service provider who may or may not allow you to get a free upgrade.
Either way this appears to be a short-run promotion and is expected to only last until the end of March 2018, which coincidentally enough is also when Apple expects iPhone 6 Plus battery replacements to be back in stock again.