Let's briefly revisit the history of HTTP to understand the context of HTTP/3's innovations:

• HTTP/0.9: The initial version, introduced in 1991, was a simple protocol for transferring raw data over the internet.
• HTTP/1.0 (RFC 1945): In 1996, HTTP/1.0 brought in structured headers and the concept of status codes, laying the groundwork for modern web interactions.
• HTTP/1.1 (RFC 2616): Introduced in 1997, it improved upon previous versions with persistent connections (keeping connections alive across requests) and caching strategies but struggled with concurrent requests.
• HTTP/2 (RFC 7540): Launched in 2015, it introduced multiplexing (concurrent/parallel request handling) and header compression, significantly improving speed and efficiency.

HTTP/3 is a substantial leap forward, primarily due to its shift from TCP (Transport Layer Security) to the QUIC (Quick UDP Internet Connections) protocol. Here are HTTP/3's standout improvements:

QUIC Protocol

The fundamental change in HTTP/3 is its use of QUIC instead of TCP. QUIC operates on top of UDP (User Datagram Protocol), which traditionally was faster but less reliable than TCP. QUIC brings the best of both worlds: the speed of UDP with added reliability and security features.

Reduced Latency

HTTP/3 significantly cuts down latency, thanks to QUIC's improved connection setup times. Unlike TCP, QUIC requires fewer round-trips (or even none, referred to as 0-RTT) to establish a connection, leading to noticeably quicker website loading times.

Solving Head-of-Line Blocking

One of the major improvements HTTP/3 brings is the resolution of the head-of-line blocking problem that was introduced in HTTP/2. In HTTP/3, packet loss affects only the specific stream it belongs to, not the entire connection. This enhancement means that a single lost packet doesn't delay the delivery of other concurrently transmitted data.

Built-In Encryption

QUIC integrates encryption and security features akin to TLS by default. This built-in encryption makes HTTP/3 inherently more secure.

Improved Congestion Control

QUIC introduces more sophisticated congestion control mechanisms. It can better navigate bandwidth fluctuations, leading to smoother and more stable connections, especially in mobile networks or less stable internet conditions.

• Browser Support: HTTP/3 is already supported by a large majority of web browsers. About 97% of tracked browser support it at least partially. Chromium browsers, like Google Chrome, Microsoft Edge, and Opera, have adopted it since April 2020 and Mozilla Firefox since May 2021. Safari also implemented HTTP/3 but is keeping it disabled by default for the time being.
• Web Usage: About 28% of the top 10 million websites have adopted HTTP/3, demonstrating its growing popularity and acceptance in the web community.
• Unsupported by Apache: While web servers such as nginx offer support for QUIC and HTTP/3, Apache (as of the time of writing) does not. The reasoning behind this can be found in the following conversation. A Feature Request (Bug #64462) for it exists.

HTTP/3 is poised to become the new norm for web traffic. Its rapid adoption by browsers and websites as well as most web servers signals a shift towards a more efficient, reliable, and secure internet.