During the long shutdown 4 of the LHC the instantaneous luminosity will be increased by a factor of $\approx 10$ to $1.5\cdot 10^{34} \text{cm}^{-2}\text{s}^{-1}$. The expected data recorded with the LHCb detector will increase from 50 $\text{fb}^{-1}$ to 300 $\text{fb}^{-1}$. This will require an upgrade of the LHCb tracking systems. For the downstream tracker this upgrade detector is referred to as the Mighty Tracker.
The innermost part of the Mighty Tracker is planned to be instrumented with monolithic CMOS sensors. The outer part will keep the scintillating fibre approach of the currently installed SciFi detector. There are several aspects that make this a unique environment for a tracking detector. The high occupancy in the high $\eta$ region of LHCb (hit rates up to 18 $\text{MHz/cm}^2$), the harsh radiation conditions ($6\cdot 10^{14} 1 \text{MeV} n_{\text{eq}}/\text{cm}^2$), the streaming readout approach with low material budget ($X/X_0<1.5\%$) requirements are just naming a few key challenges. This can be achieved by newly developed HV-CMOS sensors which can provide a high timing resolution of $\approx 3$ ns and are sufficiently radiation hard. The planned total instrumented pixel area is up to 18 m$^2$ of silicon. This paper will describe the plans for the Mighty Tracker and initial beam tests with the precursor of the MightyPix chip.