  We demonstrate microwave measurements of the Andreev bound state (ABS)
spectrum in planar Josephson junctions (JJs) defined in Ge high mobility
two-dimensional hole gases contacted by superconducting PtSiGe. The JJs and
readout circuitry are located on separate chips and inductively coupled via
flip-chip bonding. For a device with $350~\mathrm{nm}$ junction length,
spectroscopic signatures were consistent with the short-junction limit, with an
induced superconducting gap $\Delta^{*}\approx48~\mathrm{\mu eV}$ and
transmission $\tau \approx 0.94$. The interaction between the
highest-transmission ABS and the resonator was well described by a
Jaynes-Cummings model with a vacuum Rabi splitting of approximately
$6~\mathrm{MHz}$. A device with junction length of $1~\mu m$ showed an ABS
spectrum consistent with a long junction model. Time-resolved monitoring of the
readout resonator in the dispersive regime revealed gate-voltage tunable
junction parity fluctuations on the timescale of seconds. Our work indicates a
viable path towards hybrid quantum devices based on planar Ge.
