With the proliferation of online news read on devices ranging from desktops to smart watches, the need for meaningful summaries of long texts is growing. Manual summaries are labour-intensive and cannot be offered for all display sizes, whereas today's abstracts of most news texts are teasers designed to attract the reader's interest more than to provide an overview of an article's content suited to the reader's information needs. We propose responsive news summarization as a technological approach for filling this gap. Responsive news summarization provides an automatically generated content summary that has the right length for the device requesting the article, plus access to the full text. We describe the system prototype available at multisizenews.com along with the initial user study results and give an outlook on future work.