International standardBishop, Mike; Akamai. "RFC 9114: HTTP/3". rfc-editor. Retrieved 6 June 2022. (HTTP/3 also uses the completed QUIC protocol described in RFC 9000 and related RFCs such as RFC 9001)
Developed byIETF
IntroducedRFC 9114

HTTP/3 is the third major version of the Hypertext Transfer Protocol used to exchange information on the World Wide Web, alongside HTTP/1.1 and HTTP/2. HTTP/3 always runs over QUIC relying on UDP (as opposed to TCP used by earlier revisions of HTTP). QUIC specification was published as RFC 9000.[1][2] On 6 June 2022, IETF standardized HTTP/3 as RFC 9114.[3]

Protocol Stack of HTTP/3 compared to HTTP/1.1 and HTTP/2
Protocol Stack of HTTP/3 compared to HTTP/1.1 and HTTP/2

HTTP/3 uses the same semantics as the earlier revisions, including the same request methods, status codes, and message fields, but encodes them differently and maintains session state differently.

HTTP/3 has lower latency for real-world web pages, if enabled on the server, load faster than with HTTP/2, and even faster than HTTP/1.1, in some cases over 3× faster than HTTP/1.1 (which is still commonly only enabled).[4] That's in part because the TCP (of TCP/IP), is no longer used, as in the older standards.

HTTP/3 is already supported by 73% of running web browsers,[5] and according to W3Techs 25% of the top 10 million websites.[6] It has been supported by Chromium (including Google Chrome, Microsoft Edge, Samsung Internet, and Opera which are based on it, and Chrome for Android)[7] since April 2020 and by Mozilla Firefox since May 2021.[5][8] Safari 14 (on macOS Big Sur and iOS 14) has also implemented the protocol but it is disabled by default (also in Safari 15).[9]


HTTP/3 originates from an Internet Draft adopted by the QUIC working group. The original proposal was named "HTTP/2 Semantics Using The QUIC Transport Protocol",[10] and later renamed "Hypertext Transfer Protocol (HTTP) over QUIC".[11]

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".[12] Nottingham's proposal was accepted by fellow IETF members a few days later. The HTTP working group was chartered to assist the QUIC working group during the design of HTTP/3, then assume responsibility for maintenance after publication.[13]

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.[14] Firefox added support for HTTP/3 in November 2019 through a feature flag[5][15][16] and started enabling it by default in April 2021 in Firefox 88.[5][8] Experimental support for HTTP/3 was added to Safari Technology Preview on April 8, 2020[17] and was included with Safari 14 that ships with iOS 14 and macOS 11,[9] but is still disabled by default.[18] The situation remained the same with Safari 15.

Comparison with HTTP/1.1 and HTTP/2

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.




Browser support for HTTP/3
Browser Version implemented (disabled by default) Version shipped (enabled by default) Comment
Chrome Stable build (79) December 2019 87[5] April 2020[19] Earlier versions implemented other drafts of QUIC
Edge Stable build (79) December 2019 87 April 2020 Edge 79 was the first version based on Chromium
Firefox Stable build (72.0.1) January 2020 88[8] April 2021[20]
Safari Safari Technology Preview 104 April 2020  –  –


Open-source libraries that implement client or server logic for QUIC and HTTP/3 include[21]

Libraries implementing HTTP/3
Name Client Server Programming language Company Repository
lsquic Yes Yes C LiteSpeed
nghttp3 Yes Yes C
h2o No Yes C
libcurl[22][23] Yes No C
MsQuic[24] Yes Yes C Microsoft
proxygen Yes Yes C++ Facebook
Cronet Yes Yes C++ Google
.NET[25] Yes Yes C# (using MsQuic)[26] Microsoft
quic-go Yes Yes Go
http3 Yes Yes Haskell
Kwik Yes Yes Java
Flupke Yes No Java
aioquic Yes Yes Python
quiche Yes Yes Rust Cloudflare
neqo Yes Yes Rust Mozilla
quinn Yes Yes Rust


See also


  1. ^ "Cloudflare HTTP/3".((cite web)): CS1 maint: url-status (link)
  2. ^ Iyengar, Jana; Thomson, Martin (May 2021). QUIC: A UDP-Based Multiplexed and Secure Transport.
  3. ^ "HTTP/3". Retrieved 6 June 2022.
  4. ^ "HTTP/3 is Fast". Request Metrics. Retrieved 1 July 2022.
  5. ^ a b c d e "Can I use... Support tables for HTML5, CSS3, etc". Retrieved 2 May 2022.
  6. ^ "Usage of HTTP/3 for websites". World Wide Web Technology Surveys. W3Techs. Retrieved 12 February 2022.
  7. ^ "Enabling QUIC in tip-of-tree". Retrieved 8 April 2021.
  8. ^ 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.((cite web)): CS1 maint: url-status (link)
  9. ^ a b "Safari 14 Release Notes". Retrieved 4 December 2020.
  10. ^ Shade, Robbie (8 July 2016). HTTP/2 Semantics Using The QUIC Transport Protocol. IETF. I-D draft-shade-quic-http2-mapping.
  11. ^ Cimpanu, Catalin (12 November 2018). "HTTP-over-QUIC to be renamed HTTP/3 | ZDNet". ZDNet. Retrieved 12 November 2018.
  12. ^ Nottingham, Mark (28 October 2018). "Identifying our deliverables". IETF Mail Archive.
  13. ^ "Hypertext Transfer Protocol Charter". Retrieved 2 September 2020.
  14. ^ "Enabling QUIC in tip-of-tree". Retrieved 8 April 2021.
  15. ^ Daniel, Stenberg. "Daniel Stenberg announces HTTP/3 support in Firefox Nightly". Twitter. Retrieved 5 November 2019.
  16. ^ Cimpanu, Catalin (26 September 2019). "Cloudflare, Google Chrome, and Firefox add HTTP/3 support". ZDNet. Retrieved 27 September 2019.
  17. ^ "Release Notes for Safari Technology Preview 104". 8 April 2020. Retrieved 7 August 2020.
  18. ^ Ng, Gary (23 June 2020). "Apple's Safari Adds Support for HTTP3 in iOS 14 and macOS 11". Retrieved 25 June 2021.
  19. ^ "Enabling QUIC in tip-of-tree". Retrieved 9 April 2021.
  20. ^ "Firefox Release Owners - MozillaWiki". Retrieved 9 April 2021.
  21. ^ "QUIC Implementations". GitHub. Retrieved 8 April 2021.((cite web)): CS1 maint: url-status (link)
  22. ^ "First HTTP/3 with curl". Daniel Stenberg. 5 August 2019. Retrieved 2 October 2019.
  23. ^ "cURL HTTP3 wiki". Daniel Stenberg. 26 September 2019. Retrieved 2 October 2019.
  24. ^ "MsQuic is Open Source". 28 April 2020. Retrieved 28 April 2020.
  25. ^ "HTTP/3 support in .NET 6". 17 September 2021. Retrieved 17 September 2021.
  26. ^ "HTTP/3 support in .NET 6". .NET Blog. 17 September 2021. Retrieved 12 January 2022.
  27. ^ "LiteSpeed Web Server Release Log - LiteSpeed Technologies". Retrieved 12 February 2022. Enable HTTP/3 v1 by default.
  28. ^ "Release 2.0 beta 17 · caddyserver/caddy". Github. 13 March 2020. Retrieved 11 August 2020.
  29. ^ "Introducing a Technology Preview of NGINX Support for QUIC and HTTP/3". NGINX. 10 June 2020. Retrieved 11 June 2020.
  30. ^ "Experiment with HTTP/3 using NGINX and quiche". The Cloudflare Blog. 17 October 2019. Retrieved 9 November 2019.
  31. ^ Tratcher. "Use ASP.NET Core with HTTP/3 on IIS". Retrieved 29 April 2022.