426 Upgrade Required — Causes & Fix
HTTP 426 (Upgrade Required) means the server refuses the request on the current protocol and requires the client to upgrade to a different protocol (e.g. a newer TLS or HTTP version, or WebSocket).
- Applies to
- Any website or web server (HTTP standard)
- Time to fix
- 5–30 minutes
What it means
Causes include a server requiring TLS/HTTP upgrade, or an endpoint that only accepts WebSocket connections. HTTP status 426 is defined in RFC 9110 (HTTP Semantics). This is a client-side (4xx) error — the request itself had a problem, so the fix is usually on the requester's side or in how the server validates the request.
Symptoms
- "426 Upgrade Required"
- Connection rejected until the protocol is upgraded
How to fix it
- 1
Upgrade the protocol
1. Use the protocol the server requires (e.g. connect over the newer TLS/HTTP version or WebSocket).
- 2
Update the client
1. Update the client library so it supports the required protocol.
Frequently asked questions
What does 426 want me to do?
Switch to the protocol the server demands — often a newer TLS/HTTP version or a WebSocket upgrade. Update the client accordingly.
Last updated July 20, 2026
Guidance only — always consult a qualified professional or the official service manual before carrying out repairs.