HTTP3

HTTP/3 is the third major version of the Hypertext Transfer Protocol. It is built on QUIC, a transport protocol designed to run over UDP and to integrate TLS 1.3 encryption. HTTP/3 replaces TCP with QUIC as the underlying transport to reduce latency, enable multiplexed streams, and avoid head-of-line blocking at the transport layer. It introduces header compression using QPACK and uses a framing layer suitable for QUIC streams. The protocol is defined in RFC 9114, with QUIC specified in RFC 9000 and TLS 1.3 in RFC 8446; QPACK is defined in RFC 9204.

Key design characteristics include the use of QUIC as the transport, which provides zero round-trip time for repeated connections through 0-RTT handshakes (subject to security considerations), connection migration to preserve sessions when networks change, and inherent encryption for all traffic via TLS 1.3. HTTP/3 uses the ALPN token h3 to negotiate the protocol during the TLS handshake. A notable change from HTTP/2 is that HTTP/3 does not define a server push mechanism; resources are instead requested by the client as needed.

Adoption and status: HTTP/3 has broad support among major web browsers, including Chrome, Edge, Firefox, and Safari, with ongoing improvements in interoperability. Content Delivery Networks and many web servers provide HTTP/3 support, though deployment can vary by platform and configuration. In practice, servers often offer HTTP/3 alongside HTTP/1.1 and HTTP/2, with clients and networks negotiating the best available transport. Observers note that UDP-based transport can encounter blockage or interference from some middleboxes, necessitating fallback to earlier HTTP versions in certain environments.

See also: HTTP/2, QUIC, QPACK, TLS 1.3, RFC 9114.