Apple Watch 3 series no longer works with Homekit

Now that my 3 series (OS8) no longer works with Homekit, for how long will it work if i buy a series 4? A month? A year? I cant believe i have to throw away a otherwise perfectly working series 3 watch and buy a new one just to get back functionality with Homekit. Is this Apple ethics? Is this a sustainable policy? Didn’t Apple allready loose a court case on iOS upgrade issues with older devices?

[Edited by Moderator]