Projections of the background Ω_GW spectrum, given our knowledge of the compact binary population. The shaded regions outline 90% credible bands for the GWB from BBHs and BNS (in pink), including the uncertainty on the mass and redshift models for these sources using the samples released in Abbott et al. (2023a), LIGO Scientific Collaboration, Virgo Collaboration, KAGRA Collaboration (2021). For BBHs we report the uncertainty due to two mass models: the PLPP mass model, assuming a MD redshift model with uncertain local merger rate R₀ (orange), and also uncertain low-redshift power-law index γ (green); and the BPL mass model, assuming a MD redshift model with uncertain R₀ and γ. Current and projected sensitivity curves are included for reference.