I went through more than 10 rounds of interviews (including phone screening, 1:1 interviews, panel interviews, a presentation, and more panel and 1:1 interviews with the VP and CEO) over a period of more than 2 months. The onsite interviews required 3-4 hours each time to go through all of the different interview rounds set up. I also was given a presentation to complete, to be presented to a panel of 5 people, with additional questions at the end of this. I was promised I would be given feedback/ an answer in a week, but did not hear back. When I followed up, I was told they would get back to me in a couple more days. It has been four weeks since and I still haven't (and don't expect to) hear back. Feels really unprofessional after such extensive rounds of interviews, and having spent so much time on the interview process. The least you could do is respect the time and effort, and contact unsuccessful candidates to let them know they haven't made it.