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 Upgrade header with this response to indicate the required protocol(s).

Status

426 Upgrade Required

Examples

Upgrade required from HTTP/1.1

Given a GET request to a system:

GET /resources HTTP/1.1
Host: example.com

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

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

See also

• HTTP response status codes
• Upgrade
• 101 Switching Protocols