OS X 10.11.4 Release Date Announcement
After a lengthy period of testing, we expect to see the OS X 10.11.4 release date announced at this event. Odds are very good that it will come out within 24-48 hours of the iOS 9.3 release date.
This means that we should expect to see the new OS X El Capitan update potentially the same week as the event.
Apple packs in a new Notes App that supports locked notes, just like iOS 9.3, and now supports Live Photos on Mac inside the Photos app and the Messages app.
Expect this to come as a downloadable update that you can install on your Mac before the end of March.