The antonyms for the word "be the same class as" would be "be of a different class than" or "be in a separate class from." These antonyms imply a distinction or separation between two entities that differ in their social, economic, or hierarchical classification. While being of the same class usually suggests similarity, being of a different class denotes diversity or difference. For instance, a person may be of a higher or lower social class than another, or two products may belong to different price ranges, and hence, different economic classes. In any case, using antonyms of "be the same class as" allows for precise and nuanced communication about differences, inequalities, or disparities.