Aims and objectives: This study examines the extent to which new speakers use the Basque ergative case marking ( –k) in the nominal inflection. I specifically ask whether frequency-based factors (language use and lexical frequency) play a role in its use by also considering speakers’ self-claimed Basque identities. Design/methodology/approach: The spontaneous speech of 39 Basque–Spanish bilinguals was collected by means of sociolinguistic interviews. Participants were self-stratified according to categories of Basque speakerhood ( euskaldunberri “new speaker”; euskaldun “Basque speaker”; euskaldunzahar “native speaker”). We also considered their proficiency, language use, and sex. Data and analysis: In total, 2,755 tokens were extracted for the presence/absence of ergative –k and coded for the following four linguistic factors: verb type, animacy person and number, phonological context, and type of NP. Lexical frequency was operationalized in terms of overall token frequency of lexical verb. Data were analyzed using mixed-effects models in R. Findings and conclusions: Results indicate that despite higher incidence of ergative omissions among new speakers, they show (1) consistent mastery of core internal constraints (verb type, phonological context) and (2) gradual structuring based on lexical frequency effects. These omissions occur in pragmatically structured conditions (topic shift, emphasis, and introducing self in narrative) alongside extensions of –k to unaccusative contexts (focus and topicalization). No independent effects of language use were found. Originality: This study is the first to examine of Basque ergativity among adult Basque speakers, taking also into account discourse factors, lexical frequency, and speakers’ social identities and proficiencies. Significance and implications: First, the mediating effects of lexical frequency are indicative that that sociolinguistic variation is acquired in a piece-meal fashion and that such patterns emerge from discourse as they are used in context. Second, it is argued that the new speakers’ kind of social practices hold key in explaining the reallocation of linguistic constraints in their variable production.