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Background The Woven EndoBridge (WEB) device is an intrasaccular flow disruptor for treating wide-necked intracranial aneurysms. The second-generation WEB-17, introduced in 2019 and delivered via a 0.017-inch microcatheter, expands treatment to smaller, distal aneurysms compared to the original WEB-21, which needs a 0.021-inch microcatheter. Whether WEB-17 matches WEB-21 in angiographic occlusion is uncertain. This study combines a systematic review, meta-analysis, and multicenter cohort to compare the two devices.Methods We searched MEDLINE, Embase, and the Cochrane Library (January 2015-March 2026) for comparative WEB-17 versus WEB-21 studies, and collected primary individual patient data (IPD) from three North American centers (Montefiore Medical Center, Hospital of the University of Pennsylvania, and University of Iowa). The primary outcome was adequate occlusion (Raymond-Roy grade 1-2 or BOSS grade 0/2). Pooled odds ratios were estimated using random-effects models (REML, Hartung-Knapp CI), with sensitivity analyses including person-time standardization (incidence rate ratios) to address follow-up heterogeneity and rupture-stratified subgroup analysis using exact stratification by rupture status.Results Five studies comprising 580 patients (349 WEB-17; 231 WEB-21) were included. For adequate occlusion, the pooled OR was 0.66 (95% CI 0.23-1.87; p=0.33; I 2=27.8%). For complete occlusion, the pooled OR was 0.69 (95% CI 0.28-1.71; p=0.32; I2=64.9%). Person-time standardization eliminated heterogeneity for occlusion outcomes (IRR 1.04; I2=0%), confirming that between-study variance was driven by follow-up duration differences. Rupture-stratified analysis using exact stratification (k=2 per stratum) showed common-effect ORs favoring WEB-21 for complete occlusion in both unruptured (OR 0.43; 95% CI 0.22-0.83; p=0.01) and ruptured (OR 0.39; 0.16-0.91; p=0.03) strata. Pooled safety analyses showed no significant differences in thromboembolic (OR 0.76), hemorrhagic (OR 0.71), or mortality outcomes.Conclusions Current evidence does not demonstrate a significant difference in adequate occlusion between WEB-17 and WEB-21 devices. Person-time analysis confirmed that follow-up heterogeneity drove between-study variance. Rupture-stratified results suggest a possible advantage of WEB-21 for complete occlusion, though these exploratory findings require confirmation. These findings should be considered hypothesis-generating.Disclosures B. Demessie: None.Abstract E-254 Figure 1