  The four-loop determination of the strong coupling from fully inclusive
observables is reviewed. Special attention is given to the low-energy
measurement extracted from the hadronic $\tau$ decay width. A recent exhaustive
analysis of the ALEPH data, exploring several complementary methodologies with
very different sensitivities to inverse power corrections and duality
violations, confirms the strong suppression of non-perturbative contributions
to $R_\tau$. It gives the value $\alpha_s(m_\tau^2)= 0.328 \pm 0.013$, which
implies $\alpha_s(M_Z^2)= 0.1197 \pm 0.0015$. The excellent agreement with the
direct measurement at the $Z$ peak, $\alpha_s(M_Z^2)= 0.1196 \pm 0.0030$,
provides a beautiful test of asymptotic freedom. Together with the most recent
lattice average from FLAG and the NNLO determinations from $e^+e^-$, PDFs and
collider data quoted by the PDG, these two inclusive determinations imply a
world average value $\alpha_s(M_Z^2)= 0.1180 \pm 0.0010$.
