I had been wondering if that was actually something special because I thought I remembered that the German Meteorological Service ("Deutscher Wetterdienst") offered accurate forecasts on a sub-kilometer grid for years already. At least if you are ready to spend money on that because that service is not free, so maybe that's the innovation here.
Where did you get the existence of sub-km (horizontal) grid forecasts from? Thus page https://www.dwd.de/EN/research/weatherforecasting/num_modell... contains the following sentence:
"The operational NWP models of DWD currently employ horizontal grid mesh widths between 2.8 and 13 km."
The convective cell tracking for nowcasting seems finer, IMO reasonable as it's about predicting watersheds down to <10km² area flash-flooding and causing the local creek to swell to actually dangerous levels/requiring partial evacuation of a valley.
