The antonyms for "am subsequent to" can vary based on the context in which the phrase is used. However, some possible antonyms include "am preceding," "am concurrent with," or "am simultaneous with." These words refer to events or actions that occur before, at the same time or in conjunction with the main action or event. Another antonym for "am subsequent to" can be "am not relevant to," which implies that the action or event in question is not related or connected to the main subject. Ultimately, the choice of antonym will depend on the specific meaning and intention of the sentence in which the phrase appears.