According to a post that was spread on Inven OBT could be ending Dec. 5th. Not to sure on the actual dates, and specifics. However, the content that is populated in the post is actual content that is supposed to be coming to the game. Some of the highlights are new classes and 10 Man Epic Raids.
Here is the actual post that was first spread on inven, then Lost Ark Discord & Reddit: http://blog.naver.com/PostView.nhn?blogId=jmk1756&logNo=221406229009