Background and Purpose: In patients with acute large vessel occlusion, the natural history of penumbral tissue based on perfusion time-to-maximum (T _max ) delay is not well established in relation to late-window endovascular thrombectomy. In this study, we sought to evaluate penumbra consumption rates for T _max delays in patients with large vessel occlusion evaluated between 6 and 16 hours from last known normal. Methods: This is a post hoc analysis of the DEFUSE 3 trial (The Endovascular Therapy Following Imaging Evaluation for Ischemic Stroke), which included patients with an acute ischemic stroke due to anterior circulation occlusion within 6 to 16 hours of last known normal. The primary outcome is percentage penumbra consumption, defined as (24-hour magnetic resonance imaging infarct volume–baseline core infarct volume)/(T _max 6 or 10 s volume–baseline core volume). We stratified the cohort into 4 categories based on treatment modality and Thrombolysis in Cerebral Infarction (TICI score; untreated, TICI 0-2a, TICI 2b, and TICI3) and calculated penumbral consumption rates in each category. Results: We included 141 patients, among whom 68 were untreated. In the untreated versus TICI 3 patients, a median (interquartile range) of 53.7% (21.2%–87.7%) versus 5.3% (1.1%–14.6%) of penumbral tissue was consumed based on T _max >6 s ( P <0.001). In the same comparison for T _max >10 s, we saw a difference of 165.4% (interquartile range, 56.1%–479.8%) versus 25.7% (interquartile range, 3.2%–72.1%; P <0.001). Significant differences were not demonstrated between untreated and TICI 0-2a patients for penumbral consumption based on T _max >6 s ( P =0.52) or T _max >10 s ( P =0.92). Conclusions: Among extended window endovascular thrombectomy patients, T _max >10-s mismatch volume may comprise large volumes of salvageable tissue, whereas nearly half the T _max >6-s mismatch volume may remain viable in untreated patients at 24 hours.