Providing a notification in place of content item

Methods, systems, and apparatus include computer programs encoded on a computer-readable storage medium, including a method for providing content. A request for content is received from a user device. One or more candidate content items that are responsive to the request are identified from an inventory of content items. For each candidate content item, an expected performance measure associated with a respective candidate content item is determined. The expected performance measure for each respective candidate content item is compared to a predetermined threshold. When none of the candidate content items have an expected performance measure that exceeds the threshold, a notification is generated, including generating one or more queries, responsive to the request for inclusion in the notification. The notification is provided responsive to the request and for presentation to the user in lieu of a content item.