Update: Accurate determinations of αs from realistic lattice QCD

We use lattice QCD simulations, with MILC configurations ( including vacuum polarization from u, d, and s quarks), to update our previous determinations of the QCD coupling constant. Our new analysis uses results from 6 different lattice spacings and 12 different combinations of sea-quark masses to significantly reduce our previous errors. We also correct for finite-lattice-spacing errors in the scale setting, and for nonperturbative chiral corrections to the 22 short-distance quantities from which we extract the coupling. Our final result is alpha(V)(7.5 GeV; n(f) = 3) = 0.2120(28), which is equivalent to alpha((MS) over bar)(M-Z, n(f) = 5) = 0.1183(8). We compare this with our previous result from Wilson loops, which differs by one standard deviation.