Supplemental content prediction to reduce blink-in effect

Methods, systems, and apparatus, including computer programs encoded on a computer storage medium, for determining, for each of a plurality of resource requests for a resource that includes first content, whether a supplemental content event has occurred. The occurrence of the supplemental content event indicates that supplemental content will likely be served to a user device after the resource is served to the user device. For each resource request for which the supplemental content event has occurred, the resource is served with a defined supplemental content environment in which the supplemental content is to be displayed, the supplemental content environment being of dimensions that accommodate display of the supplemental content without adjustment of display of the first content upon the user device rendering the resource. For each resource request for which the supplemental content event has not occurred, the resource is served without the defined supplemental content environment.