Introduction: Hyperglycemia is common in ischemic stroke. Admission glucose modifies the effect of endovascular therapy (EVT) in patients with ischemic stroke of the anterior circulation, who are treated 0 to 6 hours since onset. Whether this also applies for late-window EVT (6–24 hours since symptom onset or last known well) is unknown. In this study, we assessed whether admission glucose level and/or hyperglycemia modifies the EVT effect in patients with ischemic stroke of the anterior circulation in the late time window. Methods: We used data from the MR CLEAN LATE trial. The primary outcome measure was the modified Rankin Scale (mRS) score at 90 days. Secondary outcome measures were symptomatic intracranial hemorrhage and mortality at 90 days. Treatment effect modification of EVT by either glucose or hyperglycemia on admission was assessed by multiplicative interaction factors with logistic regression analysis and adjusted for potential confounders. Hyperglycemia was defined as glucose level >7.8 mmol/L on admission. Results: On admission, median glucose was 7.0 mmol/L (IQR 6.0–8.3 mmol/L), and 147 patients (32%) were hyperglycemic. We found no interaction of either hyperglycemia or serum glucose on admission with treatment effect on functional outcome (p = 0.76 and p = 0.79, respectively), symptomatic intracranial hemorrhage (p = 0.29 for hyperglycemia; p = 0.57 for glucose on admission), and for mortality (p = 0.52 for hyperglycemia; p = 0.69 for glucose on admission). Conclusion: We found no evidence for effect modification of EVT by admission glucose level or hyperglycemia in patients with acute ischemic stroke and large-vessel occlusion of the anterior circulation in the late treatment window.