The dark energy from virtual gravitons is consistent with observational data on supernova with the same accuracy as the CDM model. The fact that virtual gravitons are capable of producing of a de Sitter accelerated expansion of the FLRW universe was established in 2008 (see references). The combination of conformal non–invariance with zero rest mass of gravitons (unique properties of the gravitational field) leads to the appearance of graviton dark energy in a mater-dominated era. Тhis fact explains the relatively recent appearance of the dark energy and answers the question “Why now?”. The transition redshifts (where deceleration is replaced by acceleration) that follow from the graviton theory are consistent with model independent transition redshifts derived from observational data. Prospects for testing the GCDM model (the graviton model of dark energy where G stands for gravitons) and comparison with the CDM model are discussed.