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Introduction/Purpose Passive advancement is a phenomenon observed during contact aspiration mechanical thrombectomy performed with recently available inner delivery devices. The phenomenon involves the aspiration catheter advancing distally as the inner delivery device is withdrawn, without active advancement by the operator. The vacuum created by evacuating the space occupied by the inner device is hypothesized to prime clot ingestion into the catheter tip prior to aspiration. Although anecdotally associated with favorable outcomes among experienced ASCENT users, the phenomenon has not been systematically characterized. This study aims to define passive advancement, assess its prevalence with various devices, and evaluate its association with recanalization outcomes in a consecutive-patient thrombectomy series.Materials and Methods A retrospective review of consecutive thrombectomy cases was conducted at two high-volume stroke centers from January 2022 through December 2025. Patient demographics, operator, angiographic findings, devices used, and technique performed were noted. Available fluoroscopy clips and stored procedural images were reviewed to assess aspiration catheter tip position during each pass. Passive advancement was defined as documented distal movement of the aspiration catheter tip between initiation of inner device removal and its final resting position. It was also separately noted if the final resting position of the aspiration catheter was shown to lie at a branch point on subsequent angiography. Primary outcomes were eTICI 2b-3, eTICI 2c-3, and modified first pass effect (mFPE eTICI 2c-3). Secondary occlusion was assessed as a secondary outcome. Fisher’s exact test was used for univariable comparisons; multivariable regression identified independent predictors of passive advancement.Results 684 occlusions were treated in 664 consecutive patients. Of 1,219 total passes, imaging adequate for catheter position assessment was identified for 940. Passive advancement was confirmed on 398 passes (61.2%). The final catheter tip position was at an arterial branch on 378 passes (58.2%), with passive advancement specifically to a branch point in 235 passes (36.2%). Passive advancement was associated with significantly higher eTICI 2b-3 (68.1% vs. 46.4%, p<0.0001), eTICI 2c-3 (53.3% vs. 36.1%, p<0.0001), and mFPE (58.5% vs. 10.0%, p<0.0001) compared to passes without passive advancement. Associations were further strengthened when advancement reached an arterial branch point—eTICI 2b-3 71.5% vs. 53.0%, eTICI 2c-3 57.9% vs. 40.2%, and FPE 2c-3 80.4% vs. 17.3% (all p<0.0001). Passive advancement to a branch was inversely associated with secondary occlusion (p=0.049). On multivariable analysis, passive advancement was independently associated with ASCENT technique versus stentriever or ADAPT (p<0.0001) and use of a tapered delivery device (p<0.0001).Conclusion Passive advancement of the aspiration catheter during mechanical thrombectomy is associated with superior recanalization outcomes across multiple TICI endpoints and a reduced rate of secondary occlusion. The effect is amplified when passive advancement occurs to an arterial branch point. This phenomenon is likely mediated by the vacuum generated during inner device withdrawal, which engulfs clot into the catheter tip and primes aspiration. Recognition and permissive facilitation of passive advancement should be considered an integral technical goal of mechanical thrombectomy and a key component of ASCENT technique.Disclosures M. Alexander: 2; C; Route 92 Medical, Stryker, J&J, Medtronic.. 4; C; Certus Critical Care, Route 92 Medical, Piraeus Medical, Galaxy Therapeutics. R. Khangura: None. B. Varjavand: None. T.A. Chaudhry: None. J. English: 2; C; Stryker Neurovascular. 4; C; Route 92 Medical. 5; C; Route 92 Medical. W. Kim: 2; C; Route 92 Medical, Stryker Neurovascular. 4; C; Route 92 Medical. F. Settecase: 1; C; Terumo. 2; C; Route 92 Medical, Stryker Neurovascular, Medtronic. 4; C; Route 92 Medical.