HTTP/3 explained

Comparison with HTTP/2

HTTP/3 is designed for QUIC, which is a transport protocol that handles streams by itself.
HTTP/2 is designed for TCP, and therefore handles streams in the HTTP layer.


The two protocols offer clients virtually identical feature sets.
  • Both protocols offer server push support
  • Both protocols have header compression, and QPACK and HPACK are similar in design.
  • Both protocols offer multiplexing over a single connection using streams


The differences are in the details and primarily there thanks to HTTP/3's use of QUIC:
  • HTTP/3 has better and more likely to work early data support thanks to QUIC's 0-RTT handshakes, while TCP Fast Open and TLS usually sends less data and often faces problems.
  • HTTP/3 has much faster handshakes thanks to QUIC vs TCP + TLS.
  • HTTP/3 does not exist in an insecure or unencrypted version. HTTP/2 can be implemented and used without HTTPS - even if this is rare on the Internet.
  • HTTP/2 can be negotiated directly in a TLS handshake with the ALPN extension, while HTTP/3 is over QUIC so it needs an Alt-Svc: header response first to inform the client about this fact.
  • HTTP/3 has no prioritization. The HTTP/2 approach to prioritization has been deemed too complicated, or even a downright failure, and there's work on creating a simpler take. This planned simpler scheme is also planned to be able so backport to run over HTTP/2 using HTTP/2's extension mechanism.