klimt26, Thanks for getting back to me. I understand that a smooth attendee experience is crucial, especially with such large webinar audiences and already planned events.
GoTo Webinar’s new experience is designed specifically to minimize disruption for both organizers and participants. When running a scheduled webinar, attendees do not need to download any new software; they can join directly from their web browser. This helps eliminate the downloading needed with the classic experience. When you switch to the new experience, your attendees will automatically be on the new experience as well.
Have you tested it yet? It's easy to switch to new experience and switch back to classic in the dashboard.
We are here to help in the Community with any questions and feedback when you try the new experience. Just let us know.