Comparison of and ratios for high-redshift galaxies, with SDP.81 datapoints denoted by stars. We include measurements for individual galaxies (Danielson et al. 2013; Oteo et al. 2017; Béthermin et al. 2018; Cañameras et al. 2021; Rybak et al. 2022, bullet points) and stacks (Reuter et al. 2022; Rybak et al. 2022; Hagimoto et al. 2023). We convert the J_upp ≥ 2 luminosities to HCN(1–0) following the z ∼ 0 HCN ladder from Israel (2023). The upper limits on HCN(4–3) emission in SDP.81 are consistent with recent works indicating low HCN/CO and HCN/FIR ratios in DSFGs.