HTTP 426 Upgrade Required

What is HTTP 426 Upgrade Required?

The 426 (Upgrade Required) status code indicates that the server refuses to perform the request using the current protocol but might be willing to do so after the client upgrades to a different protocol. The response must include an Upgrade header indicating the required protocol.

Common Use Cases

• Requiring TLS/HTTPS upgrade
• Requiring HTTP/2 upgrade
• Deprecating old protocol versions

# Nginx - returning 426 for non-TLS requests
server {
    listen 80;
    server_name api.example.com;
    
    return 426 "Upgrade Required";
    add_header Upgrade TLS/1.2;
    add_header Connection Upgrade;
}