426 Upgrade Required

The server refuses the request over the current protocol and requires an upgrade named in the Upgrade header.

426 at a glance

Code: 426
Name: Upgrade Required
Class: 4xx Client error
Status: IANA-registered standard code
Defined in: RFC 9110, Section 15.5.22
Cacheable by default: No by default. Caches store it only when the response carries explicit freshness (Cache-Control max-age, s-maxage or Expires).

What 426 means

426 Upgrade Required tells the client it must switch protocols (for example to TLS, a newer HTTP version, or WebSocket) before the server will process the request. The response must include an Upgrade header naming the acceptable protocol(s).

What typically causes a 426

A plain HTTP GET to a WebSocket-only endpoint: the Node.js ws library answers 426.
Servers that require HTTP/2 or a newer API protocol version.
Some services returning 426 to clients using deprecated TLS or protocol versions.

Fix it on the server

Include Upgrade, e.g. Upgrade: websocket, and Connection: Upgrade.

Fix it as a client or visitor

Use a WebSocket client (ws:// or wss://) for WebSocket endpoints, or upgrade the client library.
Behind a proxy, make sure Upgrade and Connection headers are forwarded.

Headers that go with 426

Header	Role
`Upgrade`	Required: protocols the server will accept.

Example response

HTTP/1.1 426 Upgrade Required
Upgrade: websocket
Connection: Upgrade
Content-Type: text/plain

Upgrade Required