Print Print
Reading time 7:21

International standardHypertext Transfer Protocol Version 3 (HTTP/3) (draft)
Developed byIETF
IntroducedInternet Draft as of June 2021

HTTP/3 is the third and upcoming major version of the Hypertext Transfer Protocol used to exchange information on the World Wide Web, alongside HTTP/1.1 and HTTP/2.[1]

HTTP semantics are consistent across versions: the same request methods, status codes, and message fields are typically applicable to all versions. The differences are in the mapping of these semantics to underlying transports. Both HTTP/1.1 and HTTP/2 use TCP as their transport. HTTP/3 uses QUIC, a transport layer network protocol which uses user space congestion control over the User Datagram Protocol (UDP). The switch to QUIC aims to fix a major problem of HTTP/2 called "head-of-line blocking": because the parallel nature of HTTP/2's multiplexing is not visible to TCP's loss recovery mechanisms, a lost or reordered packet causes all active transactions to experience a stall regardless of whether that transaction was impacted by the lost packet. Because QUIC provides native multiplexing, lost packets only impact the streams where data has been lost.

As of June 2021, the HTTP/3 protocol is still officially an Internet Draft but is already supported by 71% of running web browsers[2] and, according to W3Techs, 19.6% of the top 10 million websites.[3] It has been supported by Google Chrome (including Chrome for Android, and Microsoft Edge, which is based on it)[4] since April 2020 and by Mozilla Firefox since May 2021.[2][5]Safari 14 (on macOS Big Sur) has also implemented the protocol but support is hidden behind a feature flag.


HTTP/3 is an Internet Draft adopted by the QUIC working group. The original proposal was named "HTTP/2 Semantics Using The QUIC Transport Protocol",[6] and later named "Hypertext Transfer Protocol (HTTP) over QUIC".[7]

On 28 October 2018 in a mailing list discussion, Mark Nottingham, Chair of the IETF HTTP and QUIC Working Groups, proposed renaming HTTP-over-QUIC to HTTP/3, to "clearly identify it as another binding of HTTP semantics to the wire protocol ... so people understand its separation from QUIC".[8] Nottingham's proposal was accepted by fellow IETF members a few days later. The HTTP working group is chartered to assist the QUIC working group during the design of HTTP/3, then assume responsibility for maintenance after publication.[9]

Support for HTTP/3 was added to Chrome (Canary build) in September 2019 and then eventually reached stable builds, but was disabled by a feature flag. It was enabled by default in April 2020.[10] Firefox added support for HTTP/3 in November 2019 through a feature flag[2][11][12] and started enabling it by default in April 2021 in Firefox 88.[2][5] Experimental support for HTTP/3 was added to Safari Technology Preview on April 8, 2020[13] and was slated to be officially released with Safari 14 that ships with macOS 11,[14] but is still disabled by default.[citation needed]




Browser support for HTTP/3
Browser Version implemented (disabled by default) Version shipped (enabled by default)
Chrome Stable build (79) December 2019 87[15] April 2020[16]
Firefox Stable build (72.0.1) January 2020 88[5] April 2021[17]
Safari Safari Technology Preview 104 April 2020
Edge 87 April 2020


Open source libraries that implement client or server logic for QUIC and HTTP/3 include[18]

Library support for HTTP/3
Name Client Server Programming language Company Repository
http Yes Yes Rust
quiche Yes Yes Rust Cloudflare
neqo Yes Yes Rust Mozilla
quinn Yes Yes Rust
proxygen No Yes C++ Facebook
Cronet Yes Yes C++ Google
lsquic Yes Yes C LiteSpeed
nghttp3 Yes Yes C
h2o No Yes C
libcurl[19][20] Yes No C
MsQuic[21] Yes Yes C Microsoft
Quic.NET Yes Yes C#
Flupke Yes No Java
aioquic Yes Yes Python
quic-go Yes Yes Go
http3 Yes Yes Haskell


  • Litespeed Web Server supports HTTP/3 draft 32.[22]
  • Nginx support for HTTP/3 is being worked on. A technology preview of nginx with HTTP/3 support was released in June 2020.[23]
  • Cloudflare distributes a patch for nginx that integrates the quiche HTTP/3 library into it.[24]
  • The Caddy web server has experimental support for HTTP/3 as of 2.0 beta 17.[25]

There are a number of libraries that implement an older draft of the protocol or Google's versions of QUIC (e.g. Q046 used in Chrome 76), such as nghttp3.[26]

See also


  1. ^ Bishop, Mike (2 February 2021). "Hypertext Transfer Protocol Version 3 (HTTP/3)". IETF. I-D draft-ietf-quic-http. Retrieved 11 February 2021.
  2. ^ a b c d "Can I use... Support tables for HTML5, CSS3, etc". Retrieved 4 June 2021.
  3. ^ "Usage of HTTP/3 for websites". World Wide Web Technology Surveys. W3Techs. Retrieved 4 June 2021.
  4. ^ "Enabling QUIC in tip-of-tree". Retrieved 8 April 2021.
  5. ^ a b c Damjanovic, Dragana (16 April 2021). "QUIC and HTTP/3 Support now in Firefox Nightly and Beta". Mozilla Hacks – the Web developer blog. Retrieved 17 April 2021.
  6. ^ Shade, Robbie (8 July 2016). HTTP/2 Semantics Using The QUIC Transport Protocol. IETF. I-D draft-shade-quic-http2-mapping.
  7. ^ Cimpanu, Catalin (12 November 2018). "HTTP-over-QUIC to be renamed HTTP/3 | ZDNet". ZDNet. Retrieved 12 November 2018.
  8. ^ Nottingham, Mark (28 October 2018). "Identifying our deliverables". IETF Mail Archive.
  9. ^ "Hypertext Transfer Protocol Charter". Retrieved 2 September 2020.
  10. ^ "Enabling QUIC in tip-of-tree". Retrieved 8 April 2021.
  11. ^ Daniel, Stenberg. "Daniel Stenberg announces HTTP/3 support in Firefox Nightly". Twitter. Retrieved 5 November 2019.
  12. ^ Cimpanu, Catalin (26 September 2019). "Cloudflare, Google Chrome, and Firefox add HTTP/3 support". ZDNet. Retrieved 27 September 2019.
  13. ^ "Release Notes for Safari Technology Preview 104". 8 April 2020. Retrieved 7 August 2020.
  14. ^ "Apple Developer Documentation". Retrieved 4 December 2020.
  15. ^ "Can I use... Support tables for HTML5, CSS3, etc". Retrieved 9 April 2021.
  16. ^ "Enabling QUIC in tip-of-tree". Retrieved 9 April 2021.
  17. ^ "Firefox Release Owners - MozillaWiki". Retrieved 9 April 2021.
  18. ^ "QUIC Implementations". GitHub. Retrieved 8 April 2021.
  19. ^ "First HTTP/3 with curl". Daniel Stenberg. 5 August 2019. Retrieved 2 October 2019.
  20. ^ "cURL HTTP3 wiki". Daniel Stenberg. 26 September 2019. Retrieved 2 October 2019.
  21. ^ "MsQuic is Open Source". 28 April 2020. Retrieved 28 April 2020.
  22. ^ "LiteSpeed Web Server Release Log". LiteSpeed Web Server Release Log. 17 April 2020. Retrieved 26 June 2020.
  23. ^ "Introducing a Technology Preview of NGINX Support for QUIC and HTTP/3". NGINX. 10 June 2020. Retrieved 11 June 2020.
  24. ^ "Experiment with HTTP/3 using NGINX and quiche". The Cloudflare Blog. 17 October 2019. Retrieved 9 November 2019.
  25. ^ "Release 2.0 beta 17 · caddyserver/caddy". Github. 13 March 2020. Retrieved 11 August 2020.
  26. ^ "ngtcp2/nghttp3". 6 August 2020. Retrieved 7 August 2020 – via GitHub.

Edited: 2021-06-18 12:38:12