Microsoft Office blog:

As of the Office 365 for Mac September 2018 update, macOS 10.12 or later is required to update to the new version of the Office client apps for Mac and receive new feature updates.

macOS 10.12 is more commonly known as macOS Sierra. If you don’t want to update to Sierra, you’ll still be able to get support. You just won’t be able to update to the new shiny coming in September.

As part of the upcoming September 2018 update, Office 365 for Mac users on macOS 10.12 or later will receive an update from the Office 2016 for Mac client to Office 2019 for Mac in order to maintain access to new feature releases and updates.

If you use Office, keep this in mind. I’ve always found Microsoft’s penchant for embedding calendar years in a release name an odd branding choice. In a few weeks, you’ll jump from Office 2016 to Office 2019.

No matter, good to know what’s coming.