HTTP/3
Standard(HTTP/3 also uses the completed QUIC protocol described in RFC 9000 and related RFCs such as RFC 9001)
DeveloperIETF
IntrodateJune 2022

HTTP/3 is the third major version of the Hypertext Transfer Protocol used to exchange information on the World Wide Web, complementing the widely deployed HTTP/1.1 and HTTP/2. Unlike previous versions which relied on the well-established TCP (published in 1974), HTTP/3 uses QUIC (officially introduced in 2021), a multiplexed transport protocol built on UDP.[1]

HTTP/3 uses similar semantics compared to earlier revisions of the protocol, including the same request methods, status codes, and message fields, but encodes them and maintains session state differently. However, partially due to the protocol's adoption of QUIC, HTTP/3 has lower latency and loads more quickly in real-world usage when compared with previous versions: in some cases over four times faster than with HTTP/1.1 (which, for many websites, is the only HTTP version deployed).[2][3]

As of September 2024, HTTP/3 is supported by more than 95% of major web browsers in use[4] and 34% of the top 10 million websites.[5] It has been supported by Chromium (and derived projects including Google Chrome, Microsoft Edge, Samsung Internet, and Opera)[6] since April 2020 and by Mozilla Firefox since May 2021.[4][7] Safari adopted it since Sept 2024 (16+ supports HTTP3 for all users, previously it was limited to a subset of users) [8]

History

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",[9] and later renamed "Hypertext Transfer Protocol (HTTP) over QUIC".[10]

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".[11] 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.[12]

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.[6] Firefox added support for HTTP/3 in November 2019 through a feature flag[4][13][14] and started enabling it by default in April 2021 in Firefox 88.[4][7] Experimental support for HTTP/3 was added to Safari Technology Preview on April 8, 2020[15] and was included with Safari 14 that ships with iOS 14 and macOS 11,.[16][17] Starting September 2024, HTTP/3 is supported for all users on Safari 16 or newer.[8]

On 6 June 2022, IETF published HTTP/3 as a Proposed Standard in .

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.

The HTTPS DNS resource record as defined in allows for connecting without first receiving the Alt-Svc header via previous HTTP versions, therefore removing the 1 RTT of handshaking of TCP.[18][19] There is client support for HTTPS resource records since Firefox 92, iOS 14, reported Safari 14 support, and Chromium supports it behind a flag.[20][21][22]

Implementations

Client

Browser support for HTTP/3
BrowserVersion implemented (disabled by default)Version shipped (enabled by default)Comment
ChromeStable build (79)December 201987[4]April 2020[23]Earlier versions implemented other drafts of QUIC
EdgeStable build (79)December 201987April 2020Edge 79 was the first version based on Chromium
FirefoxStable build (72.0.1)January 202088[7]April 2021[24]
SafariStable build (14.0)September 202016.4September 2024Apple tested HTTP/3 support on some Safari users starting with Safari 16.4.[25]
Starting September 2024, HTTP/3 is supported for all users on Safari 16 or newer.[8]

Libraries

Open-source libraries that implement client or server logic for QUIC and HTTP/3 include[26]

Libraries implementing HTTP/3
NameClientServerProgramming languageCompanyRepository
lsquicCLiteSpeedhttps://github.com/litespeedtech/lsquic
nghttp3Chttps://github.com/ngtcp2/nghttp3
h2oChttps://github.com/h2o/h2o
libcurl[27][28]Chttps://github.com/curl/curl
MsQuic[29]CMicrosofthttps://github.com/microsoft/msquic
proxygenC++Facebookhttps://github.com/facebook/proxygen#quic-and-http3
CronetC++Googlehttps://github.com/chromium/chromium/tree/main/net/quic
.NET[30]C# (using MsQuic)[31]Microsofthttps://github.com/dotnet
quic-goGohttps://github.com/quic-go/quic-go
http3Haskellhttps://github.com/kazu-yamamoto/http3
KwikJavahttps://github.com/ptrd/kwik
FlupkeJavahttps://bitbucket.org/pjtr/flupke
aioquicPythonhttps://github.com/aiortc/aioquic
niquestsPythonhttps://github.com/jawah/niquests
quicheRustCloudflarehttps://github.com/cloudflare/quiche
neqoRustMozillahttps://github.com/mozilla/neqo
quinnRusthttps://github.com/quinn-rs/quinn
s2n-quicRustAmazon Web Serviceshttps://github.com/aws/s2n-quic

Server

  • On 7 June 2021, LiteSpeed Web Server (and OpenLiteSpeed) 6.0.2 was released and became the first version to enable HTTP/3 by default.[32]
  • Caddy web server v2.6.0 (released 20 September 2022) has HTTP/3 enabled by default.[33]
  • Nginx supports HTTP/3 since 1.25.0 (released 23 May 2023). A technology preview of nginx with HTTP/3 support was released in June 2020.[34] Binary packages of nginx with HTTP/3 support have been released in February 2023.[35]
  • Cloudflare distributes a patch for nginx that integrates the quiche HTTP/3 library into it.[36]
  • Microsoft IIS support for HTTP/3 is enabled natively with Windows Server 2022/Windows 11.[37]
  • HAProxy supports HTTP/3 over QUIC since version 2.6 released on 31 May 2022.[38][39]
  • Nimble Streamer supports HTTP/3 since 4.1.8-1[40] for HTTP-based protocols.

References

  1. ^ "What is HTTP/3?". Cloudflare. Archived 4 July 2022 at the Wayback Machine. Retrieved 12 July 2022.
  2. ^ Perna, Gianluca; Trevisan, Martino; Giordano, Danilo; Drago, Idilio (2022-04-01). "A first look at HTTP/3 adoption and performance". Computer Communications. 187: 115–124. doi:10.1016/j.comcom.2022.02.005. hdl:11368/3025202. ISSN 0140-3664. S2CID 246936473
  3. ^ "HTTP/3 is Fast". Request Metrics. Retrieved 2022-07-01.
  4. ^ ""HTTP/3" | Can I use... Support tables for HTML5, CSS3, etc". canIuse.com. Retrieved 2024-08-11.
  5. ^ "Usage of HTTP/3 for websites". World Wide Web Technology Surveys. W3Techs. Retrieved 11 August 2024.
  6. ^ "Enabling QUIC in tip-of-tree". groups.google.com. Retrieved 2021-04-08.
  7. ^ Damjanovic, Dragana (16 April 2021). "QUIC and HTTP/3 Support now in Firefox Nightly and Beta". Mozilla Hacks – the Web developer blog. Retrieved 2021-04-17.
  8. ^ Jen Simmons (2024-10-30). "Updating Safari support for HTTP3". GitHub. Retrieved 2025-07-20.
  9. ^ Shade, Robbie (8 July 2016). "HTTP/2 Semantics Using The QUIC Transport Protocol". IETF
  10. ^ Cimpanu, Catalin (12 November 2018). "HTTP-over-QUIC to be renamed HTTP/3". ZDNet. Retrieved 12 November 2018.
  11. ^ Nottingham, Mark (28 October 2018). "Identifying our deliverables". IETF Mail Archive
  12. ^ "Hypertext Transfer Protocol Charter". ietf.org. Retrieved 2020-09-02.
  13. ^ Daniel, Stenberg. "Daniel Stenberg announces HTTP/3 support in Firefox Nightly". Twitter. Retrieved 5 November 2019.
  14. ^ Cimpanu, Catalin (26 Sep 2019). "Cloudflare, Google Chrome, and Firefox add HTTP/3 support". ZDNet. Retrieved 27 Sep 2019.
  15. ^ "Release Notes for Safari Technology Preview 104". webkit.org. 8 April 2020. Retrieved 7 August 2020.
  16. ^ "Safari 14 Release Notes". developer.apple.com. Retrieved 4 December 2020.
  17. ^ Ng, Gary (23 June 2020). "Apple's Safari Adds Support for HTTP3 in iOS 14 and macOS 11". iphoneincanada.ca. Retrieved 25 June 2021.
  18. ^ "HTTPS RR". MDN. Mozilla. Retrieved 2022-10-25.
  19. ^ Schwartz, Benjamin M.; Bishop, Mike; Nygren, Erik (2020-06-12). "Service binding and parameter specification via the DNS". IETF
  20. ^ "Firefox 92 for developers". Mozilla Corporation. 7 September 2021. Retrieved 2022-10-25.
  21. ^ "Feature: HTTP->HTTPS redirect for HTTPS DNS records". Google Inc.. Retrieved 2022-10-25.
  22. ^ Patrick Mevzek (24 August 2021). "What's the use case of SVCB (type 65, service binding) RR". Stack Exchange Inc.. Retrieved 2022-10-25.
  23. ^ "Enabling QUIC in tip-of-tree". groups.google.com. Retrieved 2021-04-09.
  24. ^ "Firefox Release Owners - MozillaWiki". wiki.mozilla.org. Retrieved 2021-04-09.
  25. ^ Jen Simmons (2023-04-04). "HTTP/3 support shipped in Safari 14.0". GitHub. Retrieved 2025-07-20.
  26. ^ "QUIC Implementations". GitHub. Retrieved 2021-04-08.
  27. ^ "First HTTP/3 with curl". Daniel Stenberg. August 5, 2019. Retrieved October 2, 2019.
  28. ^ "HTTP3 (and QUIC)". Daniel Stenberg. August 23, 2023. Retrieved August 27, 2023.
  29. ^ "MsQuic is Open Source". April 28, 2020. Retrieved April 28, 2020.
  30. ^ "HTTP/3 support in .NET 6". September 17, 2021. Retrieved September 17, 2021.
  31. ^ "HTTP/3 support in .NET 6". .NET Blog. 2021-09-17. Retrieved 2022-01-12.
  32. ^ "LiteSpeed Web Server Release Log - LiteSpeed Technologies". www.litespeedtech.com. Retrieved 2022-02-12. Enable HTTP/3 v1 by default.
  33. ^ "Release 2.6.0 · caddyserver/caddy". Github. 2022-09-22. Retrieved 2022-09-20.
  34. ^ "Introducing a Technology Preview of NGINX Support for QUIC and HTTP/3". NGINX. 2020-06-10. Retrieved 2020-06-11.
  35. ^ "Binary Packages Now Available for the Preview NGINX QUIC+HTTP/3 Implementation". NGINX. 2023-02-08. Retrieved 2023-03-30.
  36. ^ "Experiment with HTTP/3 using NGINX and quiche". The Cloudflare Blog. 2019-10-17. Retrieved 2019-11-09.
  37. ^ Tratcher. "Use ASP.NET Core with HTTP/3 on IIS". docs.microsoft.com. Retrieved 2022-04-29.
  38. ^ "Announcing HAProxy 2.6". HAProxy Blog. 31 May 2022.
  39. ^ "QUIC Implementation in HAProxy". HAProxyConf video presentation. 25 January 2023.
  40. ^ "HTTP/3 and QUIC support in Nimble Streamer". NGINX. 2025-02-14. Retrieved 2025-02-17.