It’s implemented but it still requires an official Google Assistant smart home skill and a cloud connection to set-up. It works out of the box with Home Assistant Cloud.

It’s kinda cool how it works, as your Google Home Mini will run our JS app and let it interact with Home Assistant. In the case of Home Assistant Cloud, all commands are just forwarded as-is as all processing is always local. You can see the source here https://github.com/NabuCasa/home-assistant-google-assistant-...

Note, syncing local access, exposed devices and any command requiring 2FA still goes via the cloud.