Time was you could go to Microsoft’s website and get a definitive answer as to when your Surface machine’s support life cycle would end. For reasons unknown, that information isn’t where it used to be. It’s an open question whether Microsoft has unilaterally withdrawn support — a particularly important question, given the ultimate availability of Meltdown/Spectre patches.
Let’s say you have a Surface Pro 2 and you want to know if Microsoft will ever fix the Meltdown/Spectre vulnerability on your machine. To date, there’s been no notification one way or the other, but the tea leaves look increasingly bitter.