The third version of the Hypertext Transfer Proto-
col (HTTP) is in its final standardization phase by the IETF. Be-
sides better security and increased flexibility, it promises benefits
in terms of performance. HTTP/3 adopts a more efficient header
compression schema and replaces TCP with QUIC, a transport
protocol carried over UDP, originally proposed by Google and
currently under standardization too. Although HTTP/3 early
implementations already exist and some websites announce its
support, it has been subject to few studies. We provide a first
measurement study on HTTP/3 adoption and performance. We
testify how it has been adopted by some of the leading Internet
companies such as Google, Facebook and Cloudflare in 2020.
We run a large-scale measurement campaign towards thousands
of websites adopting HTTP/3, aiming at understanding to what
extent it achieves better performance than HTTP/2. We find that
adopting websites often host most web page objects on third-
party servers, which support only HTTP/2 or even HTTP/1.1.
As excepted, websites loading objects from a limited set of third-
party domains (avoiding legacy protocols) are those experiencing
larger performance gains. Our experiments however show that
HTTP/3 provides sizable benefits only in scenarios with high
latency or poor bandwidth.
