  We perform a fit of the finite-volume QCD spectrum of three pions at maximal
isospin to constrain the three-body force. We use the unitarity-based
relativistic three-particle quantization condition, with the GWUQCD spectrum
obtained at 315 MeV and 220 MeV pion mass in two-flavor QCD. For the heavier
pion mass we find that the data is consistent with a constant contact term
close to zero, whereas for the lighter mass we see a statistically significant
energy dependence in tension with the prediction of leading order ChPT. Our
results also suggest that with enough three-body energy levels, the two-body
amplitude could be constrained.
