The below article is out of date as of Nov 4 th 2019. Please check out this article for the latest OneNote announcement.
We’re incredibly lucky to have millions of passionate OneNote users aro...
It is just the new ribbon look that they are testing out. It wasn't there in OneNote 2016 originally. I've had it in Outlook/Excel/Word/etc. for a few weeks now. https://www.microsoft.com/en-us/microsoft-365/blog/2018/06/13/power-and-simplicity-updates-to-the-office-365-user-experience/?ranMID=24542&ranEAID=nOD/rLJHOac&ranSiteID=nOD_rLJHOac-kFeIDytUmcKo7.kt3756EA&epi=nOD_rLJHOac-kFeIDytUmcKo7.kt3756EA&irgwc=1&OCID=AID681541_aff_7593_1243925&tduid=(ir_w0432R3F2Vf6Q1MXzqxqhXpyUkjQzhSp0zZsUo0)(7593)(1243925)(nOD_rLJHOac-kFeIDytUmcKo7.kt3756EA)()&irclickid=w0432R3F2Vf6Q1MXzqxqhXpyUkjQzhSp0zZsUo0. I just thought for sure that they wouldn't bother upgrading the OneNote 2016 ribbon given the product is dead.
But maybe it isn't dead, and maybe they are either getting enough push back or figuring out that there is way WAY too much OneNote 2016 is capable of that they cannot possibly get into OneNote for Windows in time.