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Background The Flow Re-direction Endoluminal Device X (FRED X) is a dual-layer braided, self-expanding flow-diverting stent designed to reconstruct the parent artery and promote aneurysm thrombosis. While aneurysm occlusion is well characterized, the impact of FRED X on covered branch vessels remains incompletely defined. This study evaluates early vascular remodeling and branch vessel flow adaptation following treatment of internal carotid artery (ICA) aneurysms.Methods Single-center retrospective analysis of patients treated with FRED X between 09/2022 and 11/2024. Patients with saccular C5-C7 ICA segment aneurysms and 6-month angiographic follow-up were included. Cases without follow-up were excluded. Branch vessel coverage was analyzed with distinction between flow-diverting and non-flow-diverting FRED X stent segments. Primary endpoints included branch vessel patency and caliber changes.Results Twenty-two patients were included (mean age 57.2 years, 86.4% female) with mean aneurysm diameter 5.45 mm, neck size 3.5 mm, and dome-to-neck ratio of 1.6. Covered branch vessels included the ophthalmic artery (OphA 22/22; 20 flow-diverting, 2 non-flow-diverting), posterior communicating artery (PcomA 15/22; 7 flow-diverting, 8 non-flow-diverting), anterior choroidal artery (AChA 9/22; 2 flow-diverting, 7 non-flow-diverting), and A1 segment (2/22; both non-flow-diverting). At 6 months, one OphA (4.5%) demonstrated caliber reduction, and in one case (4.5%) the OphA was not opacified on ICA angiography with compensation via the external carotid artery. Absence of antegrade PcomA flow from the ICA was observed in 5 cases (22.7%), with an additional 2 cases (9.1%) demonstrating caliber reduction. Among these 7 cases of PcomA flow adaptation, 6 (85.7%) involved coverage by the flow-diverting segment. In one case (4.5%), the AChA was reconstituted via retrograde PcomA flow in the absence of antegrade ICA inflow to both vessels.Conclusion Early vascular remodeling after FRED X flow diversion appears common, particularly with flow-diverting segment coverage of the PcomA, and is associated with compensatory flow adaptation. Changes in covered ICA branch vessels are predominantly clinically silent. These findings suggest a strong role of local hemodynamics and Circle of Willis collateral capacity, and highlight the need to further delineate the differential impact of flow-diverting versus non-flow-diverting segments on branch vessel behavior.Disclosures F. Al-Shaibi: None. K. Darko: None. C. Schirmer: 1; C; Microvention. O. Goren: 1; C; Microvention. 2; C; Microvention. P. Hendrix: 1; C; Microvention.