Primarily its core seems to be QUIC over HTTP. They’ve been working with the IETF and Google and Mozilla on the standard.
the TL;DR
This is where HTTP/3 comes into play: instead of using TCP as the transport layer for the session, it uses QUIC, a new Internet transport protocol, which, among other things, introduces streams as first-class citizens at the transport layer. QUIC streams share the same QUIC connection, so no additional handshakes and slow starts are required to create new ones, but QUIC streams are delivered independently such that in most cases packet loss affecting one stream doesn’t affect others. This is possible because QUIC packets are encapsulated on top of UDP datagrams.
Using UDP allows much more flexibility compared to TCP, and enables QUIC implementations to live fully in user-space — updates to the protocol’s implementations are not tied to operating systems updates as is the case with TCP. With QUIC, HTTP-level streams can be simply mapped on top of QUIC streams to get all the benefits of HTTP/2 without the head-of-line blocking.
QUIC also combines the typical 3-way TCP handshake with TLS 1.3’s handshake. Combining these steps means that encryption and authentication are provided by default, and also enables faster connection establishment. In other words, even when a new QUIC connection is required for the initial request in an HTTP session, the latency incurred before data starts flowing is lower than that of TCP with TLS.
Honestly. Might be good. I’m not sure how id test out its actual improvements in any noticeable way, but perhaps this makes a lot of sense with the increasing number of mobile devices using HTTP.