ErrorFindly
4264xx Client ErrorMedium

HTTP 426 Upgrade Required

Defined in RFC 7231

What Does HTTP 426 Mean?

The server refuses to perform the request using the current protocol but might after the client upgrades to a different protocol.

Common Causes

  1. 1Server requires HTTPS but request came over HTTP
  2. 2Server requires HTTP/2 or newer protocol version
  3. 3WebSocket upgrade required for the endpoint
  4. 4API version upgrade required

Impact

  • ⚠Cannot access the resource with current protocol
  • ⚠Must upgrade connection to proceed

Developer Fix

For web developers and application engineers

  1. 1Check the Upgrade header in the response for required protocol
  2. 2Switch to HTTPS if required
  3. 3Implement protocol upgrade handling in client

Server Admin Fix

For system administrators and DevOps engineers

  1. 1Include Upgrade header indicating the required protocol
  2. 2Implement proper protocol upgrade negotiation
  3. 3Consider using redirects instead of 426 for HTTP to HTTPS

Frequently Asked Questions

When is 426 used instead of a redirect?
426 explicitly tells the client which protocol to upgrade to via the Upgrade header. For HTTP-to-HTTPS, most servers use 301 redirects instead, as it's better supported by browsers.
How do I handle a 426 response?
Check the Upgrade header in the response to see what protocol is required, then re-establish the connection using that protocol.

Related HTTP Status Codes

101Switching Protocols301Moved Permanently

About the Author

Web Infrastructure Team

Verified against official RFC specifications and real-world server configurations. HTTP status code behavior confirmed across Apache, Nginx, and Cloudflare.