Dynamically selecting and presenting content relevant to user input

Methods, systems, and apparatus, including computer programs encoded on computer storage media are provided. One example method includes receiving a textual input that forms a part of a user request, the textual input in the form of a prefix that when complete constitutes the request. The method further includes identifying completions based on the prefix, determining one or more content items associated with each completion, computing initial scores including a score for each content item-completion pair including determining a likelihood that a given completion represents the request and a quality of the content item as compared to the completion, computing final scores including scores for each prefix-content item pair using the initial scores, computing a bid for each content item, running an auction to select a content item based on the bids and final scores, and identifying display data associated with the selected content item.