Is SmartThings Classic being discontinued?

[JDRoberts]

Yes. See The official announcement thread:

Get ready to make the switch!

Hi Everyone, Many of the features from SmartThings Classic are now included in the new SmartThings app! We have started asking some users to transition to the new app. However, a few of the features you know and love might not be available quite yet. We will be releasing our transition tool to small groups over the next few weeks. Keep an eye out for the banner in the SmartThings Classic app to get started. [ClassicAppBanner] If you have not yet transitioned to a Samsung Account, follow the steps in the banner in the SmartThings Classic app to get started. Check out our FAQ for more information about the new app.