This paper tests the new-dialect formation model of Peter Trudgill (1986 et seq) by examining several phonological features of Tibetan as spoken in the diaspora community of Kathmandu, Nepal. Established by an influx of migrants from many dialect regions beginning in 1959, this presents a unique opportunity to study koinéization, new dialect formation, in progress. Trudgill’s model predicts that a new dialect should largely emerge in the second generation born in the new region, exhibiting both simplification, the failure of marked variants to transmit across generations, and focusing, the selection of particular variants as a new norm for the community's new variety.Data from seventy-three sociolinguistic interviews was coded for phonological and lexical variables known to differ across Tibetan-speaking regions, and NeighborNets were constructed in SplitsTree. Results indicate that regionally marked variables were not transmitted into the first or second generation of Diaspora-raised speakers, but Diaspora speakers exhibited a high degree of variation comparable to that of speakers from the numerically- and socially-dominant U-Tsang region. That younger speakers have not yet converged on a single new variety suggests a role for additional factors to affect the rate of koinéization.