In English-medium instruction or integrated content and language learning environments, advanced specialist writers, such as PhD candidates, may be classified as C1 level performers on the Common European Framework of Reference for Languages (CEFR). They may receive only limited linguistic support for their writing and risk incurring an impression of little progress in terms of language in their writing. This paper investigates the use of C level descriptors to identify self-efficacy in writing in three groups of early PhD candidates in two disciplines, management sciences and life sciences. The study shows an effect of institution (discipline) and confidence on the candidates’ rating of their performance of a range of advanced writing abilities. Conclusions suggest that self-efficacy and confidence ratings may help to guide the provision of writing assistance in English-medium instruction or integrated environments.