The movie is currently being filmed in Rhode Island with Emma Stone and Joaquin Phoenix in the lead roles, reported Variety online.
Allen, 78, is expected to write, produce and direct, as he has with so many of his other projects. Letty Aronson and Stephen Tenenbaum will also produce.
Plot details are currently being kept tightly under wraps.
Posey is best known for her critically-acclaimed performances in 'Kicking and Screaming', 'Best in Show' and 'Louie', while Blackley appears in the upcoming romantic drama 'If I Stay'.