HTTP/3

HTTP/3 is the newest major version of the HTTP protocol, standardized in 2022 (RFC 9114). Its most important change is invisible to users but fundamental for performance: instead of the TCP protocol that all previous versions relied on, HTTP/3 uses the QUIC transport protocol running over UDP.

How HTTP/3 works

In HTTP/2, stream multiplexing worked at the application level but was still bound by TCP — losing one packet stalled data delivery across all streams, because TCP guarantees ordered delivery. This phenomenon, called transport-level head-of-line blocking, is eliminated by HTTP/3: QUIC treats each stream independently, so a lost packet in one does not block the others. QUIC's additional advantages are:

• Faster connection setup — QUIC combines the transport handshake and TLS 1.3 encryption into a single step, and supports a 0-RTT mode on reconnection.
• Connection migration — a session is identified independently of the IP address, so switching from Wi-Fi to mobile data does not break the transfer.
• Built-in encryption — QUIC encrypts traffic by default, including much of the transport metadata.

Practical application

HTTP/3 delivers the biggest gains on networks with variable quality and high latency — on mobile devices and over long distances to the server — where it shortens TTFB and smooths out loading. It is already supported by major browsers and large CDNs, and on the server side it appears in Nginx, LiteSpeed and Caddy. Enabling it usually comes down to configuring the server or CDN and opening UDP traffic on port 443; the browser discovers HTTP/3 availability through the Alt-Svc header and seamlessly switches to the newer protocol.