HTTP/3

HTTP/3 is the latest major version of the Hypertext Transfer Protocol. It preserves HTTP semantics but replaces the underlying transport, running over QUIC, a protocol built on UDP rather than TCP.

How It Works

HTTP/2 solved application-level head-of-line blocking but still ran over a single TCP connection, so a single lost packet stalled all multiplexed streams. HTTP/3 fixes this by using QUIC, which implements independent streams at the transport layer. A lost packet only blocks the stream it belongs to, not the others.

QUIC also integrates TLS 1.3 directly into the handshake, combining transport and encryption setup so connections establish in fewer round trips. Because QUIC connections are identified by a connection ID rather than an IP and port pair, a client can move between networks, such as Wi-Fi to cellular, without dropping the connection.

Why It Matters

HTTP/3 improves performance on lossy and high-latency networks, such as mobile, where TCP's behavior hurts the most. Faster handshakes and connection migration make it well suited to today's mobile-first traffic, and major browsers, CDNs, and servers now support it widely.

The move to UDP brings challenges. Some networks throttle or block UDP, and QUIC pushes more logic into user space, which complicates tuning and observability. Deployments typically advertise HTTP/3 while keeping HTTP/2 as a fallback.

Related Terms

HTTP/3 builds on QUIC over UDP, integrates TLS, and succeeds HTTP/2 which runs over TCP.