Comparison between the inferred effective-spin support of the high-mass BBH population and the expectations for hierarchical mergers. The upper panel shows the joint posterior on ﹩{\chi }_{{\rm{eff}},{\rm{\min }}}﹩ and ﹩{\chi }_{{\rm{eff}},{\rm{\max }}}﹩ inferred from GWTC-3, GWTC-4, and GWTC-5 for the high-mass population above the transition mass scale ﹩\tilde{m}=45{M}_{\odot }﹩. The corresponding marginalized distributions are shown in the top and right panels. With the increase of the catalog size, the constraints on the extent of the χ_eff distribution have improved substantially. The data favor ﹩{\chi }_{{\rm{eff}},{\rm{\max }}}\sim 0.5﹩ and increasingly constrain ﹩{\chi }_{{\rm{eff}},{\rm{\min }}}﹩ toward values near −0.5 while strongly disfavoring both ﹩{\chi }_{{\rm{eff}},{\rm{\min }}}=-1﹩ and ﹩{\chi }_{{\rm{eff}},{\rm{\min }}}=0﹩. The dashed lines indicate ﹩{\chi }_{{\rm{eff}},{\rm{\min }}}=-0.47﹩ and ﹩{\chi }_{{\rm{eff}},{\rm{\max }}}=0.47﹩, corresponding to the characteristic support expected from hierarchical mergers. The light gray region marks the region where ﹩{\chi }_{\mathrm{eff},\min }\gt {\chi }_{\mathrm{eff},\max }﹩. The lower panel compares the inferred χ_eff distributions below and above the transition mass scale ﹩\tilde{m}﹩. The low-mass population remains sharply peaked around small positive values of χ_eff, while the high-mass population develops substantially broader support extending toward both positive and negative effective spins. The broad support of the high-mass population is consistent with expectations for binaries containing remnants of previous black hole mergers.