How is 426 different from HSTS redirect?

HSTS uses 307 redirect from HTTP to HTTPS. 426 explicitly tells the client to upgrade the protocol.

Can I ignore 426 and keep using the current protocol?

No, the server will not serve the resource over the current protocol. You must upgrade as indicated.

HTTP 426 Upgrade Required — Protocol Upgrade Needed

Warning4xx client error

Overview

HTTP 426 Upgrade Required means the server refuses to perform the request using the current protocol and requires the client to upgrade to a different protocol.

Key Details

Server requires the client to switch to a different protocol version
The Upgrade header in the response specifies which protocol to use
Common when a server requires TLS/HTTPS but receives plain HTTP
Also used for WebSocket upgrade requirements
Different from 301/308 redirects — 426 requires a protocol change, not a URL change

Common Causes

Accessing an HTTPS-only endpoint via plain HTTP
WebSocket endpoint receiving a regular HTTP request without upgrade
Server requiring HTTP/2 but receiving HTTP/1.1 request
API requiring a minimum TLS version not met by the client

Steps

1Check the Upgrade response header for the required protocol
2Switch from HTTP to HTTPS if indicated
3For WebSocket connections, ensure you send the proper Upgrade: websocket header
4Update your HTTP client to support the required protocol version
5If TLS version is the issue, update your client's TLS library