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The HTTP 426 Upgrade Required client error response code indicates that the server refuses to perform the request using the current protocol but might be willing to do so after the client upgrades to a different protocol.

The server sends an Upgrade header with this response to indicate the required protocol(s).


426 Upgrade Required


HTTP/1.1 426 Upgrade Required 
Upgrade: HTTP/3.0 
Connection: Upgrade 
Content-Length: 53 
Content-Type: text/plain 

This service requires use of the HTTP/3.0 protocol


Specification Title
RFC 7231, section 6.5.15: 426 Upgrade Required Hypertext Transfer Protocol (HTTP/1.1): Semantics and Content

See also

Document Tags and Contributors

 Contributors to this page: teoli, fscholz
 Last updated by: teoli,