A system and method for probabilistic shaping of an eight-dimensional super-symbol in optical transport networks, including receiving binary data to be transmitted as an optical signal; mapping at least a portion of the binary data to symbols of a M-QAM constellation; generating a first four-dimensional symbol of the M-QAM constellation for a first symbol period, including applying probabilistic shaping to the first four-dimensional symbol; generating a second four-dimensional symbol of the M-QAM constellation for a second symbol period, the second symbol period consecutive to the first symbol period, wherein the first and the second four-dimensional symbols have i) an equal symbol energy and ii) a one-to-one relationship; and time interleaving the first symbol period and the second symbol period to generate an eight-dimensional super-symbol.