  The nEXO neutrinoless double beta decay experiment is designed to use a time
projection chamber and 5000 kg of isotopically enriched liquid xenon to search
for the decay in $^{136}$Xe. Progress in the detector design, paired with
higher fidelity in its simulation and an advanced data analysis, based on the
one used for the final results of EXO-200, produce a sensitivity prediction
that exceeds the half-life of $10^{28}$ years. Specifically, improvements have
been made in the understanding of production of scintillation photons and
charge as well as of their transport and reconstruction in the detector. The
more detailed knowledge of the detector construction has been paired with more
assays for trace radioactivity in different materials. In particular, the use
of custom electroformed copper is now incorporated in the design, leading to a
substantial reduction in backgrounds from the intrinsic radioactivity of
detector materials. Furthermore, a number of assumptions from previous
sensitivity projections have gained further support from interim work
validating the nEXO experiment concept. Together these improvements and updates
suggest that the nEXO experiment will reach a half-life sensitivity of
$1.35\times 10^{28}$ yr at 90% confidence level in 10 years of data taking,
covering the parameter space associated with the inverted neutrino mass
ordering, along with a significant portion of the parameter space for the
normal ordering scenario, for almost all nuclear matrix elements. The effects
of backgrounds deviating from the nominal values used for the projections are
also illustrated, concluding that the nEXO design is robust against a number of
imperfections of the model.

Nuclear Experiment;Instrumentation and Detectors