HTTP/1.0 was published as RFC 1945 in May 1996. Work on the new version HTTP/1.1 was already underway, but this RFC documented the current and stable practice at that time.

HTTP/1.1 was first published in January 1997 as RFC 2068. Perhaps the biggest change compared to HTTP/1.0 was the introduction of persistent connections and pipelining. This made more efficient use of TCP/IP, and as web pages increasingly used more resources (HTML, images, CSS, scripts, etc.), this improvement significantly helped make the web faster.

In June 1999, RFC 2616 was published, improving the specification of HTTP/1.1 but not representing a new version of HTTP. RFC 2616 remained the reference specification for 15 years.

As RFC 2616 was rather long and sometimes difficult to read, and work on a new version of HTTP had begun, a series of RFCs was published in June 2014 to replace RFC 2616. This series continued to standardize HTTP/1.1 and included RFCs 7230–7235. RFC 7231 was a “semantics” document, focused on what HTTP concepts like request methods, header fields, and status codes mean, without addressing their specific representation “on the wire” in HTTP/1.1.

The clarified HTTP semantics enabled the development of new wire formats, which happened with the publication of HTTP/2 as RFC 7540 in May 2015. This protocol was originally known as SPDY and introduced binary representations and multiplexing of interactions on a TCP connection, resulting in significant performance improvements over HTTP/1.1.

Timeline of HTTP protocol development with RFC numbers and features, such as 1945 (HTTP/1.0, 1996), 2616 (HTTP/1.1, 1999) and 9114 (HTTP/3, 2022), against a purple background.
Timeline of HTTP Standards 1996-2022

In June 2022, a new series of RFCs was published, RFC 9110 to 9114. RFC 9110 defines HTTP semantics and is now the reference for HTTP concepts. RFC 9112 is an updated version of HTTP/1.1. RFC 9113 is an updated version of HTTP/2. RFC 9114 is a new version of HTTP, HTTP/3, which makes further performance improvements by replacing TCP with another transport protocol: it uses UDP along with a relatively new protocol, QUIC, which improves the transfer of multiple independent streams.

It’s likely that the RFC 9110 to RFC 9114 series of documents will now remain stable for several years. Much work has gone into improving previous documents and aligning all three wire formats of HTTP. The web and HTTP-based APIs can now transition from the old HTTP/1.1 to HTTP/2 (still based on TCP), and eventually to HTTP/3, which uses QUIC over UDP. This transition will take some time, and during this transitional period, these latest documents will determine how the web operates.

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