HTTP 426 Upgrade Required

What it means

Upgrade Required describes how the server processed the request and what the client should do next.

Why it happens

Common triggers include protocol conditions, routing decisions, and application behavior.

Common causes

• Malformed request format
• Authentication or authorization mismatch
• Missing resource or route

How to fix it

• Validate request URL, method, and headers
• Fix authentication/authorization flow
• Correct client payload and retry

Example request/response

GET /example HTTP/1.1
Host: errorlookup.com

HTTP/1.1 426 Upgrade Required

Browser/dev/server context

Use browser network tools, server logs, and APM traces together when diagnosing HTTP 426.

Related status codes

FAQ

Is HTTP 426 officially assigned?

Yes. This code is assigned in the IANA registry.