The phrase "what is in to" implies curiosity, interest or involvement with a particular subject matter. Antonyms for this phrase would include indifference, disinterest, and detachment. If someone is "not in to" a topic, it means they lack passion or engagement towards it. Likewise, if something is "out of one's league" or "over their head", it suggests that they are not knowledgeable or experienced enough to fully grasp the subject matter. Conversely, someone who is "in the know" or "in the loop" has a high level of familiarity and interest in the topic at hand.