---
set: 4
code: 426
title: Upgrade Required
references:
    "Rails HTTP Status Symbol": ":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 server MUST send an
Upgrade header field in a 426 response to indicate the required protocol(s)
(Section 6.7 of RFC7230][2]).

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.
```

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>