The Inner Tracker upgrade for the CMS experiment at HL-LHC.

The high-luminosity upgrade for the LHC (HL-LHC) is expected to deliver up to 200 pp collisions at $14 {TeV}$ every $25 {ns}$, greatly increasing the potential for physics research and new discoveries. Close to the interaction point, the density and rate of produced particles will reach values beyond $1 {GHz/cm^2}$, with detectors experiencing unprecedented levels of radiation. For operation in these much harsher conditions, development is ongoing at CMS for a new silicon tracking detector in place of the one currently installed in the experiment. The new detector will feature a more extended coverage up to $|\eta| = 4$, a lower material budget and trigger capabilities. In the region of the detector volume closest to the beamline, where operating conditions are the most extreme, the Inner Tracker is going to employ high-granularity ({25\times 100 $\mu m^2)$ pixel technology, enabled by innovative sensors and by the CROC, the chip for their readout, specifically designed in $65 {nm}$ CMOS technology by the RD53 collaboration for use at the HL-LHC. In this contribution, the state of the project for the upgrade of the Inner Tracker at large will be discussed, with highlights from CROC-related development.