Q. I am writing an annotated bibliography. My article has 4 authors. Do I need to site all the authors in the annotated bibliography?

APA does not have a guide for creating an annotated bibliography. Usually an annotation would be attached to a citation. You would definitely list all four authors in this "ur-citation."

Annotations need to be concise. It would seem to make sense that you would use an abbreviated form of the names. Perhaps you might even just be able to refer to them as the "authors." We would automatically know who they are because of your initial citation.

Since there is no guide for me to answer this question with, I would defer this style question to your professor.