1. A method comprising, by one or more computing systems: receiving a request from a first user for content comprising a plurality of objects; receiving a user identifier for the first user and a content context, the content context comprising a list of one or more other users the first user is associated with; filtering the plurality of objects based on the received content context; obtaining user features for the user identifier; obtaining object features for each of the filtered objects; calculating, via a recommendation model, an expected value for each of the filtered objects based on the user features and the object features; ordering the filtered objects by decreasing expected value; and delivering one or more of the filtered objects to the first user.