The 1xx class of status codes represents informational responses defined in RFC 9110. These codes serve specific protocol-level purposes: 100 Continue allows clients to receive acknowledgment before sending potentially large request bodies (controlled via the Expect header), preventing unnecessary data transfer if the server would reject the request. 101 Switching Protocols enables protocol upgrades, most notably from HTTP/1.1 to WebSocket connections. 102 Processing (WebDAV) indicates the server is working on a lengthy request. 103 Early Hints allows servers to send preliminary headers (like Link headers for preloading) before the final response, improving page load performance by enabling browsers to start fetching resources earlier. Implementation requires careful handling as not all clients support all 1xx codes.
