Every HTTP version exists to fix a bottleneck the last one created. The whole arc takes a few minutes.
HTTP/0.9 (1991)
The entire protocol was one line:
GET /index.htmlThe server sent back raw HTML and closed the connection. No headers, no status codes, no other methods. That was it.
HTTP/1.0 (1996)
Added the things you think of as HTTP: headers, status codes (200, 404), Content-Type so you could send images and not just HTML, and methods beyond GET. The flaw: one request per TCP connection. Every image on a page paid for a fresh handshake.
HTTP/1.1 (1997)
Made connections persistent, so many requests reuse one TCP connection, and required the Host header, which let one server host many sites. Responses still come back in request order, so one slow response blocks the rest. Browsers worked around it by opening ~6 connections per origin.
HTTP/2 (2015)
Went binary and added multiplexing: many requests and responses interleaved over a single connection, killing the 6-connection hack. Plus header compression. But it still rides TCP, and TCP delivers bytes in order, so one lost packet stalls every stream. Head-of-line blocking just moved down a layer.
HTTP/3 (2022)
Dropped TCP for QUIC, which runs on UDP (see TCP vs UDP). Each stream is independent at the transport layer, so a lost packet only blocks its own stream. The handshake is faster, and a connection survives switching networks (wifi to cellular) instead of breaking.
| Version | Year | What it added |
|---|---|---|
| 0.9 | 1991 | GET, raw HTML, nothing else |
| 1.0 | 1996 | Headers, status codes, content types |
| 1.1 | 1997 | Persistent connections, Host header |
| 2 | 2015 | Binary framing, multiplexing, header compression |
| 3 | 2022 | QUIC over UDP, independent streams |
The pattern is one chase: every version pushes head-of-line blocking down a layer. 1.1 fixed connections, 2 fixed the HTTP layer, 3 fixed the transport itself.