The High Luminosity upgrade of the CERN Large Hadron Collider (HL-LHC) calls for new high-radiation tolerant silicon pixel sensors,
capable of withstanding, in the innermost tracker layer of the CMS experiment, fluences up to $1.5\times10^{16}\,\mathrm{n_{eq}cm^{-2}}$ (1 MeV equivalent neutrons) before being replaced.
An extensive R&D program aiming at 3D pixel sensors, built with a top-side only process, has been put in place in CMS in collaboration with FBK (Trento, Italy) and CNM (Barcelona, Spain) foundries.
The basic 3D cell size has an area of $25\times100$ $\mathrm{\mu m^2}$ and is connected to a readout chip through a single, central electrode.
A number of sensors were interconnected with the CMS pixel ReadOut Chip (CROC): built in 65 nm technology, the chip will be used in the pixel tracker of the CMS experiment during HL-LHC operations.
In this paper the first test beam results of irradiated 3D CROC modules are reported.
The analysis of collected data shows excellent performance and hit detection efficiencies close to 99% measured after a fluence of $1\times10^{16}\,\mathrm{n_{eq}cm^{-2}}$ while meeting the noise occupancy requirements of the innermost tracker layer.