Ante dated implies that a document or action has been given a date earlier than the actual one. Antonyms for it can be post date, which means to assign a date later than the original one, or contemporaneous, which refers to something happening at the same time as another event. Another antonym is up-to-date, which describes something that is current and has the latest information. Similarly, modern and newfangled can also be used as antonyms for antedated, indicating something that is recent or up-to-date. In contrast, outdated and archaic describe something that is old-fashioned or obsolete.