Essentially the existing services will be replaced, same times either side of the river. Only real difference is instead of terminating / starting at Kings Cross the GN passengers will be going into St Pancras instead of King’s Cross. I assume there will be some kind of public comms about it, not sure to what extent though.Can they do that as a soft launch? Presumably it requires not running the equivalent services into Kings Cross and London Bridge, so they'd have to notify people and make it official?
For those who like to look through the planners to find these things, they won’t show up at the moment. Based on current plans (which may hopefully change) the existing services will show up as cancelled and the replacements will be at the same time but with their new destination and calling pattern.