Upgrade Required

Client Error

The client should switch to a different protocol

Server requires client to upgrade to TLS or HTTP/2

How this status code appears in HTTP responses

HTTP Response Header

HTTP/1.1 426 Upgrade Required

cURL Example

curl -I https://example.com
# Returns: HTTP/1.1 426 Upgrade Required

This is a client error response indicating the request contains bad syntax or cannot be fulfilled.

Other codes in the same category

The server cannot process the request due to client error

Authentication is required and has failed or has not been provided

Reserved for future use in digital payment systems