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In January 2023, Wikipedia introduced its most significant user interface (UI) redesign in over a decade, aiming to improve readability, accessibility, and navigation across devices. Despite the scale of this change, little empirical work has assessed its actual impact on user behavior. This study employs a natural experiment framework, leveraging Wikipedia’s exogenous, site-wide redesign date and large-scale, publicly available data—including clickstream, pageview, and edit histories—to evaluate user experience before and after the change. Using a quasi-experimental design, we estimate an immediate jump of ~1.06 million monthly internal link clicks at launch, while average hourly pageviews in January rose 1.25% despite a one-time –1.79 million dip at rollout. These results highlight the potential of large-scale UI changes to reshape user interaction without broadly alienating users and demonstrate the value of quasi-experimental methods for Human–Computer Interaction (HCI) research. Our approach offers a replicable framework for evaluating real-world design interventions at scale.