How is new economic knowledge produced over time? That depends on how the expertise of authors is managed within economic journals. Using data from 41 major economics journals spanning 21 years (1994–2014), we find that both the intensive margin (article length) and extensive margin (article number) of the discipline have been growing. In particular, the extensive margin has outgrown the intensive margin, such that each article produces absolutely more but relatively less knowledge. This pattern is highly consistent with a model of within‐journal specialization. As predicted by the model, the share of an individual article shrinks less in general interest journals and in more prestigious journals, where expertise is less substitutable across topics.