MIME type for msgpack?

According to a quick Google the overwhelming answer is application/x-msgpack. However, I can't find an authorative source.

application/x-msgpack is probably the correct MIME header, however a small caution to future readers: relying on a MIME type for anything beyond high-level information is dangerous (at best) because the structure and meaning of the message is dynamic in nature.

From Wikipedia : According to RFC 6838 (published in January 2013 : https://www.rfc-editor.org/rfc/rfc6838), any use of types in the "x." tree is strongly discouraged. Media types with names beginning with "x-" are no longer considered to be members of this tree since January 2013.

Then use directly application/msgpack