A system to control delivery of supplementary content via digital assistants, comprising: a data processing system comprising memory and one or more processors; a digital assistant component of the data processing system to: receive, via a network, data packets from a computing device comprising voice input detected by a microphone of the computing device; process the data packets to generate an action data structure that is responsive to the voice input; generate content selection criteria for input into a content selector component to select supplementary content provided by a third-party content provider, the content selection criteria comprising one or more keywords and a digital assistant content type; transmit a request to the content selector component to select supplementary content based on the content selection criteria, in a manner that overlaps with the generation of the action data structure that is responsive to the voice input; receive, responsive to the request, prior to completing the generation of the action data structure, a supplementary content item selected by the content selector component based on the content selection criteria generated by the digital assistant component; determine to delay delivery of the supplementary content item until completion of generation of the action data structure; provide, responsive to the generation of the action data structure, the action data structure and the supplementary content item to the computing device; provide, in a first graphical user interface slot via a display device coupled to the computing device, the action data structure responsive to the voice input; and provide, in a second graphical user interface slot via the display device coupled to the computing device, the supplementary content item selected by the content selector component. a data processing system comprising memory and one or more processors; a digital assistant component of the data processing system to: receive, via a network, data packets from a computing device comprising voice input detected by a microphone of the computing device; process the data packets to generate an action data structure that is responsive to the voice input; generate content selection criteria for input into a content selector component to select supplementary content provided by a third-party content provider, the content selection criteria comprising one or more keywords and a digital assistant content type; transmit a request to the content selector component to select supplementary content based on the content selection criteria, in a manner that overlaps with the generation of the action data structure that is responsive to the voice input; receive, responsive to the request, prior to completing the generation of the action data receive, via a network, data packets from a computing device comprising voice input detected by a microphone of the computing device; process the data packets to generate an action data structure that is responsive to the voice input; generate content selection criteria for input into a content selector component to select supplementary content provided by a third-party content provider, the content selection criteria comprising one or more keywords and a digital assistant content type; transmit a request to the content selector component to select supplementary content based on the content selection criteria, in a manner that overlaps with the generation of the action data structure that is responsive to the voice input; receive, responsive to the request, prior to completing the generation of the action data structure, a supplementary content item selected by the content selector component based on the content selection criteria generated by the digital assistant component; determine to delay delivery of the supplementary content item until completion of generation of the action data structure; provide, responsive to the generation of the action data structure, the action data structure and the supplementary content item to the computing device; determine to delay delivery of the supplementary content item until completion of generation of the action data structure; provide, responsive to the generation of the action data structure, the action data structure and the supplementary content item to the computing device; provide, in a first graphical user interface slot via a display device coupled to the computing device, the action data structure responsive to the voice input; and provide, in a second graphical user interface slot via the display device coupled to the computing device, the supplementary content item selected by the content selector component.