Married partner moving in 1 year after my arrival

Hello everyone!
I’ve been wondering is it possible for my partner, unmarried by now, to move in UK after me (up to 1 year after my arrival)? Everything says that it is legal and possible, but I was questioning it for a long time.
Does anyone know what duration of visa my partner should apply for in this case?

It’s possible. They have to apply based on the time left in your visa