“Soon”.
Presumably shortly before or after “soon”, the Samsung SmartThings developer documentation website will be updated.
I’m not being facetious - Stuff happens at SmartThings whenever stuff happens at SmartThings. There is no pre-published dates. That’s why the answer to when = “soon”.
In the meantime, you can still use the Groovy API:
e.g.,
https://docs.smartthings.com/en/latest/device-type-developers-guide/zigbee-primer.html