---
set: 4
code: 426
title: Upgrade Required
references:
    "Rails HTTP Status Symbol": ":upgrade_required"
    "Symfony HTTP Status Constant": "Response::HTTP_UPGRADE_REQUIRED"
---

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 server MUST send an Upgrade header field in a 426 response to indicate the required protocol(s)<sup>[1](#ref-1)</sup>

Example:

```
HTTP/1.1 426 Upgrade Required
Upgrade: HTTP/3.0
Connection: Upgrade
Content-Length: 53
Content-Type: text/plain

This service requires use of the HTTP/3.0 protocol.
```

---

* <span id="ref-1"><sup>1</sup> Upgrade [RFC7230 Section 6.7][2]</span>
* Source: [RFC7231 Section 6.5.15][1]

[1]: <http://tools.ietf.org/html/rfc7231#section-6.5.15>
[2]: <http://tools.ietf.org/html/rfc7230#section-6.7>