They don't retain IP addresses beyond 48 hours but they may retain other information (permanently). For example, the domain requested, your ISP and your approximate location (city or region).

https://developers.google.com/speed/public-dns/privacy

So, while it can't be traced back to you, it is absolutely useful information for their business. Why do you think they offer the service? To be nice?

This guarantee is one TOS change away from vanishing...

Then they'd need to announce that to all of the users of their DNS service.

You tell me how to do that.

They'd do it the same way every web service since the beginning of the internet has done it.

"By using service X you are agreeing to be bound by the terms located at .... "

Changing privacy policies doesn't work that way. You have to inform users of the changes, or they can claim that they didn't know and aren't bound by it.

That's why whenever companies change their ToS you get email/notifications/actual mail informing you of the changes.

You can't do that for DNS.

> Changing privacy policies doesn't work that way.

Legally speaking, yes it does. It's a free service. The only obligation they have is to make their terms freely accessible, and to publicize any major changes.

You seem to be implying that Google and other free DNS providers have never changed their privacy policies since there's no good way to notify the users. Google's own website (and the Internet Archive) totally contradict this.

https://developers.google.com/speed/public-dns/privacy

"Last updated October 29, 2018."

> They guarantee they don't.

They claim that they don't. You have no way of knowing if they're lying or not, though, so it boils down to "do you trust Google?"

You do, and that's fair. I don't, and that's also fair.