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426 Upgrade Required

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The HTTP 426 Upgrade Required client error response status code indicates that the server refused 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 {{HTTPHeader("Upgrade")}} header with this response to indicate the required protocol(s).

Status

http
426 Upgrade Required

Examples

Upgrade required from HTTP/1.1

Given a GET request to a system:

http
GET /resources HTTP/1.1
Host: example.com

The origin server expects that requests must be made in HTTP/3:

http
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.

Specifications

{{Specifications}}

See also