If the same URL can serve different content types shoud Vary include accept?

Question

If the same URL can serve different content types for the same resource, must Vary include Accept ? Or do browser caches and proxies understand it as being implicit ?

Example:

GET /some/thing HTTP/1.1
Accept: application/json

This response

HTTP/1.1 200 OK
Transfer-Encoding: gzip
Content-Type: application/json
Cache-Control: max-age=3600, must-revalidate
Vary: Transfer-Encoding

{...}

or this one

HTTP/1.1 200 OK
Transfer-Encoding: gzip
Content-Type: application/json
Cache-Control: max-age=3600, must-revalidate
Vary: Transfer-Encoding, Accept

{...}

Answer 1

Actually the RFC does not indicate any kind of "implict" or special treatment of the content type (Accept) header...

A Vary field value consisting of a comma-separated list of names indicates that the named request header fields, known as the selecting header fields, might have a role in selecting the representation.