Embodiments of the disclosed technologies receive a first signal from a user session and create a first ranked list of content items. Based on the first signal, a first subset of the first ranked list is assigned to a first set of slots of the user session. A second subset of the first ranked list is assigned to a second set of slots of the user session. Based on user activity data and position context data, a second ranked list of content items is created. The second ranked list is assigned instead of the second subset to the second plurality of slots.