Ferroelectric aluminum scandium nitride (Al1-xScxN, AlScN) offers CMOS-compatible integration but suffers from high coercive fields and leakage currents that hinder thickness scaling. Further reduction in thickness is essential for low-voltage embedded nonvolatile memory applications. Boron incorporation into AlScN (AlBScN) suppresses leakage current in films down to 40 nm, yet its ferroelectric characteristics in ultrathin films remain unexplored. This letter demonstrates robust ferroelectric switching in 10 nm sputtered AlBScN capacitors with a low coercive field and approximately two orders of magnitude lower leakage than AlScN. Notably, The coercive field (Ec) extracted from capacitance-voltage measurements was 2.3 MV/cm, and the onset of symmetric polarization reversal was observed near 4.6 MV/cm in positive-up-negative-down (PUND) measurements using 2 μs pulses. Moreover, the breakdown field (EBD) was determined to be 10.0 MV/cm for 10 μm diameter capacitors, suggesting a substantial margin between EBD and Ec for reliable operation. These findings demonstrate AlBScN as a promising candidate for CMOS back-end-of-line (BEOL) compatible ferroelectric applications with improved energy consumption and reduced leakage current.