  We present an update on the ongoing calculations by the Fermilab Lattice,
HPQCD, and MILC Collaboration of the leading-order (in electromagnetism)
hadronic vacuum polarization contribution to the anomalous magnetic moment of
the muon. Our project employs ensembles with four flavors of highly improved
staggered fermions, physical light-quark masses, and four lattice spacings
ranging from $a \approx 0.06$ to 0.15 fm for most of the results thus far.
