Yes. 4xx codes are client errors: The request contains a mistake or can't be fulfilled as sent.

4xx · Client error

HTTP 431 Request Header Fields Too Large

The headers, or one of them, are too big. Often caused by oversized cookies.

Example response

HTTP

HTTP/1.1 431 Request Header Fields Too Large
Content-Type: application/json; charset=utf-8

{ "error": "Request Header Fields Too Large" }

Look up the headers shown here in the HTTP headers reference.

What does HTTP 431 mean?: Request Header Fields Too Large. The headers, or one of them, are too big. Often caused by oversized cookies.
Is 431 an error?: Yes. 4xx codes are client errors: The request contains a mistake or can't be fulfilled as sent.