The linguistic situation in the Arab world is in an important state of transition, with the “spoken” vernaculars increasingly functioning as written languages as well. While this fact is widely acknowledged and the subject of a growing body of qualitative literature, there is little quantitative research detailing the process in action. The current project examines this development as it is occurring in Tunisia: I present the findings from a corpus study comparing the frequency of Tunisian Arabic–Standard Arabic equivalent pairs in online forum posts from 2010 with those from 2021. The findings show that the proportion of Tunisian lexical items, compared to their Standard Arabic equivalents, increased from a minority (19.7%) to a majority (69.9%) over this period. At the same time, metalinguistic comments on the forum reveal that, although its status is still contentious, Tunisian has become unmarked as a written language. These changes can be attributed to major developments in Tunisian society over the period of study – including internet access and the 2011 revolution. These findings suggest destabilization of the diglossic language situation in Tunisia and a privileging of national identity vis-à-vis the rest of the Arab world.