Nest requires the internet and Google cloud connection in order to work. They can just shut it off at any time.
You might be thinking of Google recently announcing that they’re no longer supporting older Nest thermostats. Not because they’re broken or anything, they just decided it was too much work for them so those people who bought a working and still perfectly good thermostat should just go ahead and give them more money.
Because they decided.
Never buy a Google product.