Front desk · HTTP Status Codes
4×× Client Error
426 Upgrade Required
· filed 2026-07-18 · click a code to copy
HTTP 426 Upgrade Required is a client error-class status code defined in RFC9110. The client must upgrade to a different protocol to continue.
Client-error responses signal that the problem is on the requesting side: the request is malformed, unauthorized, or aimed at something that isn't there. On the wire, the response begins with the status line HTTP/1.1 426 Upgrade Required.