Twitter is once again trying out carousel ads, this time with a new format which would provide those running app install campaigns with the opportunity to add multiple images for context.
Twitter is testing the Image App Carousel Card. pic.twitter.com/OaxV67MvJs
— Sam ???? (@Hooray) May 17, 2019
As you can see in this example (via Sam Schmir), the new format would enable app advertisers to include multiple, swipeable images in a single ad. It's not clear if this format would be made available for all campaign types, but it does provide more opportunity to showcase various features/elements, and would likely grab more attention in feeds.
Twitter's tried several variations of carousel ads over the years.
Back in 2016, Twitter tested a new carousel format which enabled advertisers to attach several tweets to a promotion, which users could swipe through.

That never seemed to catch on, while the company tried a similar variation of the same a year earlier, which also seemed to fade out. It makes sense for Twitter to introduce a variation of the option, given it's become a popular ad tool on other networks, but thus far, none of the iterations it's tried have seemed to gain traction with brands.
This one does look different, and it does appear to provide a more stand out, visual presence, though it's hard to say whether it'll be the version which enables the platform to capitalize on the carousel format, given previous failures. It seems more simple, less cluttered than Twitter's previous attempts. It's not as busy as the promoted tweet carousel in the example above, while it also seems to align better with evolving, side-scrolling user habits, in relation to Stories and even within Twitter's own app (Twitter added its swipe left function to access the new camera back in March).
So it could be a winner, it could be an effective new ad format, if released. We'll keep you updated on any official announcements.