New sign-in experience for Office 365, what's it about?

Thank you both for the responses. We are an EDU tenant if that makes a difference. If anything we tend to get some features later than others, even set to first-release. It might just be that we are finally catching up to a change that hit other tenants months ago.

One change this week is that our Azure/o365 admin applied new licenses to everyone. I wonder if that triggered something? Even before that we saw some pretty significant changes in some screens, especially the window that appears after you click to share a file or folder with someone. 

I don't think it is anything local to my computer, because it is affecting multiple users. So far those of us who have noticed are set up for Multifactor Autentication. I will check with some of our users who are not yet enabled for MFA.

Sean