As yet and Up to

As yet adverb - Used in negative statement to describe a situation that has existed up to this point or up to the present time.

Up to and as yet are semantically related. In some cases you can use "Up to" instead an adverb phrase "As yet".

Up to adjective - Busy or occupied with.

As yet and up to are semantically related. Sometimes you can use "As yet" instead an adverb phrase "Up to".