  A new generation of 3D silicon pixel detectors with a small pixel size of
50$\times$50 and 25$\times$100 $\mu$m$^{2}$ is being developed for the HL-LHC
tracker upgrades. The radiation hardness of such detectors was studied in beam
tests after irradiation to HL-LHC fluences up to $1.4\times10^{16}$
n$_{\mathrm{eq}}$/cm$^2$. At this fluence, an operation voltage of only 100 V
is needed to achieve 97% hit efficiency, with a power dissipation of 13
mW/cm$^2$ at -25$^{\circ}$C, considerably lower than for previous 3D sensor
generations and planar sensors.
