In the original architecture, almost everything in Smartthings was cloud dependent. You couldn’t even change the mode without an Internet connection.
Overtime, they have increased the number of things that can run locally, but it’s still pretty limited under the old architecture. And in particular anything that was custom ran in the cloud.
Now they’ve announced a new architecture, edge, and more automations can run locally. But we don’t have all the details and it’s still in transition. Right now, the app still requires an active Internet connection and we haven’t been told one way or the other whether that will continue to be true.
So right now it’s confusing for everyone. And we’re all reluctant to read anything into the statements they do make because they promised us “local processing” once before, in the transition from the V1 hub to the V2 hub, and that turned out to be almost nothing.
And the new stuff has a lot of discussion about “API First “which would include a lot of cloud cloud integrations and some cloud hosted custom smart apps.
So we just don’t know yet.
If you want a system that you can be sure can run without the Internet except for away from home control, I would look at hubitat, Homeseer, or Vera from Ezlo.
And If you know that what you want is Zwave only, I would look at Homeseer or vera.
Smartthings has always put its own abstraction layer over the top of the independent third-party protocols like Z wave, and that has led to some significant gaps. See, for example, the following:
Smartthings is a good candidate for people who want multiple protocols, including at least some matter support. But if you know you’re going to limit your setup to zwave, I don’t think it makes the top three. Mostly because of those gaps.
On the other hand, if you want a system that can run your Samsung smart television plus a lot of other cloud based devices from major brands, then smartthings would be a better candidate.
JMO of course.