We implemented the DNS-over-TLS specification along with the RFC 7766 recommendations to minimize the overhead of using TLS. These include support for TLS 1.3 (for faster connections and improved security), TCP fast open, and pipelining of multiple queries and out-of-order responses over a single connection. All of this is deployed with Google’s serving infrastructure which provides reliable and scalable management for DNS-over-TLS connections.

https://security.googleblog.com/2019/01/google-public-dns-now-supports-dns-over.html