up on vs au fait

up on and au fait both are adjectives.

Word	Noun	Adjective	Verb	Adverb
up on	No	Yes	No	No
au fait	No	Yes	No	No

As adjectives, up on and au fait are synonyms defined as:

up on and au fait: being up to particular standard or level especially in being up to date in knowledge

Other synonyms of up on include abreast, au courant.

up on (adjective)	au fait (adjective)
being up to particular standard or level especially in being up to date in knowledge	being up to particular standard or level especially in being up to date in knowledge