Little confused what is going on here, just found the new API docs and wondered if anyone could explain it or point me to somewhere that does?
I assume they have cleaned up all their APIs etc and started again but yet retain backwards compat between classic and connect? Much like the app tries to do?
There is no guaranteed backward compatibility between classic and the new app. There are features that have been removed altogether. And each version of the app has a feature called “smart home monitor” but they are completely independent of each other and work somewhat differently. There are other incompatibilities as well.
See the following thread for that discussion (the title is clickable link).
As far as the new development platform, no guaranteed backward compatibility there, either. But it’s not finished yet, so all you can do now is test stuff with it.
And the last time I looked, one of the things that was unfinished was any way to communicate with A zigbee or Z wave device connected to the hub. That is, they have not yet released the details of whatever the new equivalent of device type handlers will be for those protocols.
The documentation for the classic platform is at the following link:
https://docs.smartthings.com/en/latest/
At the top of that page is a link to the new developer portal with the documentation on what they have done with the new platform so far.
Use the following page in the new developer portal to request notification once they have completed the integration process for a “hub connected” device.
Isn’t that subject to definition?
As far as I am aware, many Device Handlers written in Groovy, including customized ones, designed for Classic App, will still provide basic operation in New App - they just need to have some correct Metadata.
Furthermore, Custom SmartApps (Groovy), mostly require using the Classic App to install them, but once installed, they can be configured and removed using either App.
My bad-- The dictation dropped a word and I missed it. It should have been “no guaranteed backward compatibility.” I’ve fixed my post above. Thanks for calling it out. 
Thank you JDRoberts (as always it seems!).
Yeh that is an interesting direction. It definitely needed a cleanup but this is a strong move. I do hope the add the ability to comm with zwave and ZigBee in the new API if they are going to push users over.
Most of my devices appear in the new connect app but there is 1 I custom wrote to control a door lock that doesn’t appear. It would be nice if they would show this fact in the dev portal and any missing method, errors etc. I.e an idea of how to resolve the issue.
Smartthings is in the middle of a huge transition: new hub, new app, and new cloud platform.
It’s helpful to remember that the new app and the new cloud platform are independent development projects. At the present time the new app obviously does work with the older cloud platform, but it limits some of the choices, particularly those controlling security features, very significantly. It’s not really clear yet whether they will need yet a newer app for the new platform or what.