The High Luminosity Large Hadron Collider (HL-LHC) at CERN is expected to collide protons at a center-of-mass energy of 14 TeV and reach the unprecedented peak instantaneous luminosity of $7 \times 10^{34}\, \mathrm{cm}^{-2}\mathrm{s}^{-1}$. This will allow the ATLAS and CMS experiments to each collect integrated luminosities of up to 4000 $\mathrm{fb}^{-1}$ during the project lifetime. To cope with this extreme scenario the CMS detector will be substantially upgraded before starting the HL-LHC, a plan known as the Phase-2 upgrade. The entire Inner Tracker (IT) detector will be replaced and the new detector will feature increased radiation hardness, higher granularity and capability to handle higher data rates. The detector is composed of pixel sensors with a pixel size of 2500 $\mathrm{\mu\mathrm{m}}^2$ and a new ASIC, designed in 65 nm CMOS technology, powered using a novel serial scheme. The system mechanics will be lightweight, based on carbon fiber, and will use a CO${}_2$ cooling scheme. In this contribution, we describe the design of the IT system along with the latest results on prototype system testing.