Designed to be fast - The Outlook on the web user experience gets simpler and more powerful - Microsoft Tech Community - 234909
Starting next week, if you are a Targeted Release customer who wants to try the early version of the new Outlook on the web, simply click on the “Try the new Outlook” toggle on the top right corner of your inbox. When you click the toggle, you’ll see all new Outlook on the web modules for Mail, Calendar, and People. Opt-in and out as often as you want.