We Chat (a.k.a., WeiXin) is a popular mobile instant messenger (MIM) with various social features and has most of its users in China. Whereas recent scholarship suggests that MIMs could support users to "dwell" together with close friends and family members and to have "fleeting" encounters with strangers, little else is known about We Chat use. In this paper, we present findings from a qualitative investigation of We Chat use and its impact on Chinese social practices. Drawing from 36 interviews conducted between 2013 and 2015, we provide a contextualized account of how We Chat use reinforces, reconfigures, and enhances existing Chinese social practices. We propose a new theoretical concept, space collapse-that denotes the emergence of a fourth space where public, private and parochial social spaces are collapsed together in a socio-technical system. We discuss how these results deepen our understanding of MIMs.