  We present the results on the relativistic six-pion scattering amplitude at
low energy, calculated at $\mathcal{O}(p^4)$ within the framework of the
massive $\text{O}(N)$ nonlinear sigma model extended to the next-to-leading
order in the chiral counting. For $N=3$, this approach corresponds to the
two(-quark)-flavor Chiral Perturbation Theory. We also present the expressions
for the pion mass, pion decay constant and the four-pion amplitude in the case
of $N$ (meson) flavors at $\mathcal{O}(p^4)$.
