Brazilian Portuguese (BP) presents a complex direct object system due to the presence of anaphoric null direct objects. Speakers of BP use a combination of animacy and specificity features to appropriately use anaphoric null direct objects (Schwenter and Silva, 2003). A learnability issue arises in acquiring this system because it involves an interface phenomenon that depends on discourse structure, semantics, and syntax. To observe whether heritage and L2 speakers of BP possess a grammar that includes anaphoric null objects, a truth-value judgment task was employed. The test was adapted from Pérez-Leroux et al. (2008). In the experimental conditions, two pictures were used to create an ambiguous context, presented to participants with both textual and auditory input. The experimental items had two possible interpretations: a transitive interpretation that favored the anaphoric null direct object or an intransitive interpretation that favored the action denoted by the verb. Three groups of participants took part in the task: a control group of native BP speakers, a group of heritage speakers, and a group of adult L2 learners. Results show that native speakers have a significant preference for the anaphoric null object interpretation. Heritage and L2 speakers do not statistically differ from the control group, also showing a bias toward the anaphoric null object interpretation. A chi-square test showed no significant differences between groups. These results are interpreted as evidence of the early acquisition of semantic-syntax v interface phenomena. The findings are consistent with Pérez-Leroux et al.’s (2018) proposal of default transitivity and the Multiple Grammar theory, which predicts access to sub-grammars.