The story format is similar to that used by the likes of Snapchat and Instagram. It takes AMP - beloved by Google but not necessarily others - beyond its basic function of making pages load faster on mobile devices.
Google has been collaborating on an open source project to develop the format with a group of top publishers - CNN, Conde Nast, Hearst, Mashable, Meredith, Mic, Vox Media, and The Washington Post.
“The collective desire was that this format offer new, creative and visually rich ways of storytelling specifically designed for mobile.“
https://developers.googleblog.com/2018/02/amp-stories-bringing-visual.html
AMP stories are designed to provide fast loading, immersive, tappable full screen content. It’s a mobile-focused format for delivering news and information with visually rich elements and flexibility in design.
With the developer preview now launched, AMP stories are available for anyone to try out on their website. There’s a tutorial and you can see more AMP stories by going to g.co/ampstories on your mobile device and searching for one of the participating publishers.
See more details on Google's AMP page and in their Developer Blog post.
