HTTP 426 Upgrade Required

What HTTP 426 means

The server names the required protocol in an Upgrade header, for example a newer TLS version or WebSocket. Some WebSocket servers return 426 when a plain HTTP request hits a WebSocket-only endpoint.

Retrying

No. Fix the request first; sending it again unchanged will get the same response.

Example response

HTTP/1.1 426 Upgrade Required
Date: Wed, 21 Oct 2026 10:30:00 GMT
Upgrade: websocket
Connection: Upgrade
Content-Type: application/json

How to return 426

res.status(426).json({ error: 'Upgrade Required' });

from fastapi import HTTPException

raise HTTPException(status_code=426, detail="Upgrade Required")

http.Error(w, http.StatusText(http.StatusUpgradeRequired), http.StatusUpgradeRequired)

location /private/ {
    return 426;
}

Related status codes

• 101 Switching Protocols : The server agrees to switch to the protocol the client asked for, such as WebSocket.
• 505 HTTP Version Not Supported : The server doesn’t support the HTTP version used in the request.

Other 4xx status codes

400 Bad Request · 401 Unauthorized · 402 Payment Required · 403 Forbidden · 404 Not Found · 405 Method Not Allowed · 406 Not Acceptable · 407 Proxy Authentication Required · 408 Request Timeout · 409 Conflict · 410 Gone · 411 Length Required · 412 Precondition Failed · 413 Content Too Large · 414 URI Too Long · 415 Unsupported Media Type · 416 Range Not Satisfiable · 417 Expectation Failed · 418 I’m a Teapot · 421 Misdirected Request · 422 Unprocessable Content · 423 Locked · 424 Failed Dependency · 425 Too Early · 428 Precondition Required · 429 Too Many Requests · 431 Request Header Fields Too Large · 444 No Response · 451 Unavailable For Legal Reasons · 499 Client Closed Request

See the full list of HTTP status codes.

Sources

• RFC 9110, section 426
• IANA HTTP Status Code Registry
• MDN: 426 Upgrade Required

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Frequently asked questions