It depends. In many flats the kitchen is part of the flat, in some it isn't. We have lived in both - I grew up in one where the kitchen was part of the flat and

It depends. In many flats the kitchen is part of the flat, in some it isn't. We have lived in both - I grew up in one where the kitchen was part of the flat and in the last flat we lived in the kitchen was not part of the flat, astonishingly the kitchen of our neighbours was part of the flat. Usually old flats ("Altbauwohnung") and flats for rich people (they want their own designer stuff) don't have the kitchen included. Other flats have, especially for people with mid or low income. Also when the flat is owned by a cooperative ("Genossenschaft") or state owned association ("Wohnungsbaugesellschaft") as many flats in Germany are. If the kitchen is not part of the flat and you move out, some owners will make you remove the kitchen, some won't. In the second case the new renter usually pays for the kitchen ("Abstandszahlung") to own it.