Humans can hear well beyond the 8 kHz ceiling of the clinical audiogram, yet hearing at extended high frequencies (EHFs, 10 to 16 kHz) can be substantially impaired even when conventional thresholds are entirely normal. This raises a basic question: is EHF loss simply an inaudible edge case, or does it index something functionally meaningful about the auditory system? Across a series of studies in young adults with normal audiograms, we found that: 1) EHF impairment was common, present in roughly one in five listeners aged 19 to 38, and was associated with subtly poorer conventional thresholds even after accounting for age. 2) EHF impairment was not confined to audibility. EHF impaired listeners showed reduced spatial release from masking and poorer speech recognition in multi talker babble, along with poorer frequency change detection at 4 kHz but not at 0.5 kHz, pointing to frequency specific deficits in suprathreshold processing rather than a global decline. 3) EHF impaired listeners also reported poorer everyday hearing on the Speech, Spatial, and Qualities of Hearing Scale, despite clinically normal audiograms. 4) Cognitive ability moderated the effects of EHF loss on suprathreshold performance, indicating that individuals with reduced cognitive capacity are particularly vulnerable to the perceptual effects of subclinical cochlear damage. 5) A 24 month follow up showed greater subsequent decline in conventional frequency thresholds among EHF impaired adults than their EHF normal peers. Together, these findings suggest EHF hearing is not merely an extension of the audiogram but a sensitive marker of individual differences in auditory resolution, spatial hearing, speech in noise perception, and vulnerability to future decline. If a threshold measured beyond the range of everyday listening can forecast both suprathreshold function and hearing trajectory, the audiogram's 8 kHz ceiling may be missing more than it captures.