The simplest nontrivial amplitude in planar $\mathcal{N}=4$ super-Yang-Mills
theory is six-gluon scattering in the maximally-helicity-violating configuration. It has been computed to 8 loops with the help of antipodal duality, which relates it to the three-point form factor of a protected operator, the chiral stress tensor super-multiplet, represented also as ${\rm tr} \phi^2$. In this talk, we describe the computation to 8 loops of another three-point form factor, for the operator ${\rm tr}\phi^3$. This form factor lives in the same restricted
space of polylogarithms as the ${\rm tr}\phi^2$ form factor. We also report on all-order patterns for sequences of coefficients in the symbols of these
polylogarithmic results, for the leading discontinuity of the ${\rm tr}\phi^3$ form factor.