To make the base game compatible with the new German Ruhr Sieg Nord (TSW:RSN) Steam is downloading 281 MB to my game.
Here is DTG's blurb on the new route and trains: https://dovetailgames.kayako.com/News/NewsItem/View/148/train-sim-world-ruhr-sieg-nord--out-now
Changelog later, if at all when no changes were made to the content already present ....