Apple will support the model up to (approx.) 5 years from last unit sold by them.

After that they will declare it as obsolete model. They will still support it whichever they could. New softwares might no longer run on such model. When the model reach 10 years or more, they will be listed as obsoletes model. By then Apple will not give any support.

https://support.apple.com/en-us/HT201624