I ordered a Montreal, Maine & Atlantic Standard Cupola Caboose directly from Atlas and saw it was cancelled on their production schedule page. So I emailed them to be sure and they told me:
Due to a factory closing in China production of the O Master Standard Cupola Caboose has been canceled. Please look for a new announcement of this item in the near future.
My order is officially cancelled and will have to place a new one when it is available again.