During the next LHC Long Shutdown 3 in 2026--2028, the ALICE Collaboration plans to replace the three innermost layers of the current Inner Tracking System (ITS) with truly cylindrical layers, made of wafer-scale, thin ($< 50~\upmu$m), and bent Monolithic Active Pixel Sensors (MAPS) that will be produced with the 65 nm CMOS imaging process. To fabricate the wafer-scale sensors, a technology, called stitching, is utilized to ``stitch'' small reticles and build sensors up to 300 mm in length in a single wafer. The upgrade aims to decrease the material budget of the innermost layers from the present 0.35\% of $X_{0}$/layer to 0.05\% of $X_{0}$/layer, essentially reducing it to the silicon contribution only. The upgraded ITS will improve the pointing resolution in the transverse plane by a factor of 2 and increase the reconstruction efficiency for low-$p_{\text{T}}$ tracks. The construction of this detector encompasses many cutting-edge R\&D efforts, for instance, production and characterization of the MAPS in the 65 nm CMOS process, fabrication of the stitched wafer-scale MAPS, and development of an ultra-light detector mechanics and a new air cooling system. This contribution provides a brief overview of the ALICE ITS3 detector and the R\&D achievements, mentioned above.