The Quintom scenario (derived from the words quintessence and phantom, as in phantom energy) is a hypothetical model of dark energy.

In this scenario, the equation of state ${\displaystyle p=w\rho }$ of the dark energy, relating its pressure and energy density, can cross the boundary ${\displaystyle w=-1}$ associated with the cosmological constant. The boundary separates the phantom-energy-like behavior with ${\displaystyle w<-1}$ from the quintessence-like behavior with ${\displaystyle w>-1}$. A no-go theorem shows that this behavior requires at least two degrees of freedom for dark energy models involving ideal gases or scalar fields.^[1]

The Quintom scenario was applied in 2008 to produce a model of inflationary cosmology with a Big Bounce instead of a Big Bang singularity.^[2]