HTTP/1.1 is the second major version of the Hypertext Transfer Protocol (HTTP), standardized in 1997 as RFC 2068 and later updated in RFC 2616 in 1999. It addressed many of the limitations of its predecessor, HTTP/1.0, by introducing persistent connections, which allowed multiple requests and responses to be sent over the same TCP connection without reopening it for each request. This enhancement significantly improved performance and reduced network overhead, making it more efficient for loading web pages with multiple resources like images, stylesheets, and scripts. HTTP/1.1 also added support for chunked transfer encoding, enabling servers to send dynamically generated content without knowing its size in advance.
HTTP/1.1 further expanded functionality by introducing cache control mechanisms (e.g., ETags and Cache-Control headers) to optimize performance and reduce redundant data transfers. It also supported content negotiation, allowing clients and servers to select the most appropriate content format based on language, encoding, or media type preferences. Additionally, it introduced pipelining, which allowed clients to send multiple requests without waiting for each response, although this feature saw limited adoption due to implementation complexities. Despite being succeeded by HTTP/2 and HTTP/3, HTTP/1.1 remains widely used and serves as the backbone for much of the modern web, demonstrating its durability and adaptability over decades.