I’ve got an older nest learning thermostat and am using the current integration. It works but sometimes the api times out and it’s obviously not local. I know there are other local thermostat options but the family likes the aesthetic and is comfortable with how to use it.
I’m wondering if the newer nest thermostat that supports matter is supported as a matter device and would be 100% local. I think It should work but If anyone can confirm that would be helpful.
I am guessing that the lack of responses means that no one really knows. If I get a chance to test this I will report back.
Interesting question – did you get an answer or managed to test this yourself?
I have not coughed up the cash to test this.
Fair enough 
According to this article it seems likely!
https://9to5google.com/2023/05/11/nest-thermostat-homekit-matter-set-up/
Don’t know, if the device still works after you cut the Internet connection though…
I really like the design, maybe I’ll give this a try in the future
Just got done replacing my Filtrete Radio Thermostat CT50 with local API (which worked but continuously had connection time outs with HA but worked pretty well. When they killed the RadioThermostat App, that is when I started using HA in home “production” environment .
I put in a Venstar Color Thermostat T7900. This device has a bult in secured API. I got it setup and connects very easily to HA once I figured our I has to setup the local API on the device.
Have not severed access to the internet yet but the local API it fast and very responsive in HA so far
