They killed the teapot!

https://www.rfc-editor.org/rfc/rfc9110.html#name-418-unused

They at least reserve 418 so that it won't get used for anything else.

But it looks like they don't list 451, defined in RFC 7725: https://datatracker.ietf.org/doc/html/rfc7725

We return 418 in a few places at work for endpoints that are only accessible to employees and you are not logged in. It’s a silly little Easter egg. Shame to see it going away.

Pretty sure you're supposed to return a 403 in any case. It'd be a nicer easter egg when sending some nonsensical but carefully chosen arguments to said endpoints.

Hmm, yeah, it's a 403 unless you are passing correct arguments but not logged in (which you'd only know if you were an employee or had access to the documentation).

Time for an RFC for HTTP 42 I’m a bowl of petunias.

I’d prefer HTTP 442 “Oh no, not again.”