Seems like Sway has now made it into my Office 365 tenant as you can see from the apps launcher at the top of Office 365.
You will also find some control options under Service Settings, Sway as shown above.
so when you go to Sway, which is a web based application, and sign in with your Office 365 credentials, you’ll be taken to the Sway portal at:
but as you can see from the above screen shot you can still navigate to any Office 365 using the app launcher.
Given what I see here and Sway having a free offering, it wouldn’t surprise me if we see some premium Sway features arrive and be included with Office 365 plans. Just speculating mind you.
So if you have Office 365, have a look and see whether you can Sway yet. if you can, give it a go.