Studies investigating how newcomers influence incumbent group members have shown equivocal performance outcomes. To disambiguate these effects, I propose and test the idea that a high-performing newcomer’s impact on incumbents’ performance flows through changes in incumbents’ communication networks. Using a proprietary dataset from a large retail bank that includes employees’ personnel records, monthly performance, and meta email communications, I argue and find that the arrival of a high-performing newcomer has differential effects on high- vs. low-performing incumbents. Specifically, following the entry of a high-performing newcomer, low-performing incumbents communicate with a smaller and more concentrated network of colleagues and subsequently perform worse than before the newcomer’s arrival. By contrast, high-performing incumbents communicate with a more extensive and diverse network and subsequently perform better. This paper draws out a mechanism underlying intra-group performance variation that is not considered in prior research: incumbents’ communication networks change following inbound mobility and subsequently exaggerate intragroup performance disparities.