  We report on the recent completion of the three-loop calculation of the soft
anomalous dimension in massless gauge-theory scattering amplitudes. This brings
the state-of-the-art knowledge of long-distance singularities in multi-leg QCD
amplitudes with any number of massless particles to three loops. The result
displays some novel features: this is the first time non-dipole corrections
appear, which directly correlate the colour and kinematic degrees of freedom of
four coloured partons. We find that non-dipole corrections appear at three
loops also for three coloured partons, but these are independent of the
kinematics. The final result is remarkably simple when expressed in terms of
single-valued harmonic polylogarithms, and it satisfies several non-trivial
constraints. In particular, it is consistent with the high-energy limit
behaviour and it satisfies the expected factorization properties in
two-particle collinear limits.
