  We present the IMRPhenomXHM frequency domain phenomenological waveform model
for the inspiral, merger and ringdown of quasi-circular non-precessing black
hole binaries. The model extends the IMRPhenomXAS waveform model, which
describes the dominant quadrupole modes $\ell = |m| = 2$, to the harmonics
$(\ell, |m|)=(2,1), (3,3), (3,2), (4,4)$, and includes mode mixing effects for
the $(3,2)$ spherical harmonic. IMRPhenomXHM is calibrated against hybrid
waveforms, which match an inspiral phase described by the effective-one-body
model and post-Newtonian amplitudes for the subdominant harmonics to numerical
relativity waveforms and numerical solutions to the perturbative Teukolsky
equation for large mass ratios up to 1000.
  A computationally efficient implementation of the model is available as part
of the LSC Algorithm Library Suite.
