Cosmological data reveal a dark energy with a negative equation of state w=P/ρ<0. We discuss its stability under nucleation from Λ>0 to Λ=0 in an assumed first-order phase transition. From arguments about stimulated nucleation it is shown that the critical nucleation radius must be at least of galactic size. The spontaneous nucleation rate is infinitesimal thus explaining the dark energy's extreme stability. Dark energy detection at subgalactic scales will never be possible.