QUIC is a new networking transport protocol that combines the features of TCP, TLS, and more. HTTP/3 protocol that carries the vast majority of Web traffic runs over QUIC.

The QUIC transport protocol has several features that are desirable in a transport for HTTP, such as stream multiplexing, per-stream flow control, and low-latency connection establishment.

HTTP/3 and IETF QUIC
Chrome is deploying HTTP/3 and IETF QUIC

QUIC protocol has matured, and is now responsible for carrying over a third of Google traffic says David Schinazi – Chrome QUIC Tech Lead

QUIC was initially developed by Google and first announced in 2013. Since then, the protocol has matured, and is now responsible for carrying over a third of Google traffic. In 2015, Google brought QUIC to the IETF (the standards organization responsible for maintaining the Internet’s protocols) and the IETF has been improving QUIC by making many changes to it. At this point, there are now two similar but different protocols: Google QUIC and IETF QUIC. The QUIC team at Google has been involved in the IETF process from the start, but we’ve been using Google QUIC in Chrome while working on implementing IETF QUIC. We’ve put tremendous effort into evolving Google QUIC over the last five years to track changes at IETF, and the current latest Google QUIC version (Q050) has many similarities with IETF QUIC. But up until now, the majority of Chrome users didn’t communicate with IETF QUIC servers without enabling some command-line options.

Chromium Blog

According to W3Techs, HTTP/3 is used by 7.4% of all the websites. Chrome is rolling out support for IETF QUIC (specifically, draft version h3-29). Today 25% of Chrome Stable users are using h3-29, company plans on increasing that number over the coming weeks.

Initially published on: Chromium Blog

References:

https://en.wikipedia.org/wiki/HTTP/3

https://quicwg.org/base-drafts/draft-ietf-quic-http.html