Prolonged management of critical illnesses in long-term acute care hospitals (LTACH) makes serious illness communication (SIC), a clinical imperative. SIC in LTACH is challenging as clinicians often lack training and patients are typically unable to participate-making caregivers central. This qualitative descriptive study characterized caregiver engagement in SIC encounters, while considering influencing factors, following the implementation of Ariadne Labs' SIC training at a LTACH in the Northeastern United States. Clinicians' documented SIC notes (2019-2020) were analyzed using directed content analysis. Codes were grouped into four categories generated from two factors that influence SIC-evidence of prognostic understanding (yes/no) and documented preferences (yes/no)-and caregiver engagement themes identified within each category. Across 125 patient cases, 251 SIC notes were analyzed. In the presence of prognostic understanding and documented preferences, caregivers acted as upholders of patients' wishes (29%). With prognostic understanding but undocumented preferences, caregivers were postponers of healthcare decision-making (34%). When lacking prognostic understanding but having documented preferences, caregivers tended to be searchers, intent on identifying continued treatment options (13%). With poor prognostic understanding and undocumented preferences, caregivers were strugglers, having difficulty with the clinicians or family unit over healthcare decision-making (21%). The findings suggest that two factors-prognostic understanding and documented preferences-are critical factors clinicians can leverage in tailoring SIC to meet caregivers' SIC needs in the LTACH setting. Such strategies shift attention away from SIC content alone toward factors that influence caregivers' ability to meaningfully engage in SIC to advance healthcare decision-making.