Basic question Regarding ecobee integration

Third party integrations
1

Does all communication between HA and the ecobee go through ecobee.com?

I think yes but am not sure.

Thanks

2

Well, it depends. lol

There are actually two different ways to connect HA and an Ecobee thermostat. If you connect via the HomeKit integration, that is a direct local connection that does not go through the ecobee website. However, if you use the native integration, then yes, that goes through the ecobee website.

There are pros and cons for each - and they can actually both be used at the same time. See this thread for a comparison of the two methods.