We’ve now updated Summary Cards on iOS & Android so people can see rich previews of website content in their timelines. Through testing and experimentation, the new design and layout has proven to drive more high quality traffic to content on your websites. Because we’ve opted to simplify the design, today we are confirming that app install and deep-linking for Summary Cards has been disabled.
If you currently have your site marked up for Summary Cards with app install and deep-linking, don’t worry! No immediate action is required on your part. You do not need to change any meta tags on your website. Your Cards will simply link to the URL containing the Twitter Card markup. You Cards will also benefit from increased exposure by being expanded in timeline. Along with app installs and deep-linking support for these new Summary Cards, we have a bunch of other features we are evaluating. Expect to hear more soon!
Product Manager for Twitter Cards