I am now fan of the included stem. It weights 350g and no internal cable routing option towards the fork but on top (so you need a bento box to hide the cables going down.
Has someone some other options? I am looking at the enve aero road stem. Much lighter. But I don't want the cables external. I prefer cables through the base bar directly to the stem and then with the top cap downwards to the fork/frame. You think this is possible?

Delayed reply of a few months here...

The stem quality is reasonable but yes its a single block of aluminium which has been machined. The cable routing is ok but yes it relies on the Profile bento being immediately behind it to hide the cables. On my build this is useful as that is also where the Di2 control box sits - easy to access for charging etc. I also use the bento to store long distance tri nutrition (salt tabs etc if I miss an electrolyte bottle or cramping). Profile do another bento (similar design) but that incorporates a 300ml gel bottle. The fork on the WINOW comes with a steerer tube length that would permit use of a normal stem (mine is now cut down as the clamp part of the WINOW stem is relatively short in height). Some stems are available with internal routing but the frame entry points are immediately behind it so I don't know how you would route the cables without seeing them slightly.

On a previous CN TT bike (made by Miracle bike) I swapped the stem out for a standard stem but no internal routing was possible and also that meant the stem didnt fit with the fork profile.

Bike still going strong - no issues as yet!