Usability is a core concept in HCI and is a common quality attribute for the design and evaluation of interactive systems. However, usability is a fluid construct and requires context-specific frameworks to be clearly defined and operationalized. Academic search user interfaces (SUIs) include the search portals of academic and research libraries, digital data repositories, academic data aggregators, and commercial publishers. In addition to information lookup, academic SUIs serve scientific information seeking in learning, exploration, and problem-solving. Researchers in library and information science (LIS) have intensively studied information seeking behavior. In recent years, exploratory search has gained attention from LIS researchers and experimental SUI features are prototyped to support information seeking. In the meantime, many academic and research libraries have conducted usability evaluation and adopted discovery systems as part of SUIs. However, there is a lack of context-specific usability models for guiding academic SUI implementation and evaluation. This study takes the perspectives of information seeking tasks and usability contextualization to propose a formative conceptual framework of academic SUI usability. Information seeking tasks from information seeking and behavior models are integrated based on the exploratory search paradigm. Information seeking tasks are mapped to the layered usability construct to shows how academic information seeking tasks may be supported to achieve high usability. Future studies should focus on developing contextualized academic SUI usability models with measurement metrics to guide the empirical implementation and evaluation of academic SUIs.