Hello, I have worked with a template on Wikipedia that uses OSM data to visualize the Metro lines. The northern part of Berlin U-Bahn U6 is not represented.
Apparently that is obvious in this relation: link
Please also see the swedish discussion here for sample map: wikipediadiskussion
It appears that the tracks are mapped as being under construction e.g. Way: 14350341 | OpenStreetMap but I don’t see anything that would say “this is a part of U6 under reconstruction” specifically