  $U(1)^\prime$ extensions of the standard model with generation-dependent
couplings to quarks and leptons are investigated as an explanation of anomalies
in rare $B$-decays, with an emphasis on stability and predictivity up to the
Planck scale. To these ends, we introduce three generations of vector-like
standard model singlet fermions, an enlarged, flavorful scalar sector, and,
possibly, right-handed neutrinos, all suitably charged under the $U(1)^\prime$
gauge interaction. We identify several gauge-anomaly free benchmarks consistent
with $B_s$-mixing constraints, with hints for electron-muon universality
violation, and the global $b \to s$ fit. We further investigate the complete
two-loop running of gauge, Yukawa and quartic couplings up to the Planck scale
to constrain low-energy parameters and enhance the predictive power. A
characteristic of models is that the $Z^\prime$ with TeV-ish mass predominantly
decays to invisibles, i.e. new fermions or neutrinos. $Z^\prime$-production can
be studied at a future muon collider. While benchmarks feature predominantly
left-handed couplings $C_9^{\mu}$ and $C_{10}^{\mu}$, right-handed ones can be
accommodated as well.
