Twitter is testing a brand new ad format for their fleets feature. This will be the first time advertisers have been able to run full screen ads on the platform.
Fleet ads will be 9:16 aspect ratio, and they will allow image or 30 second videos. They will also feature a swipe up for your chosen call to action. They will appear between fleets of different users. However, they are currently only visible to a limited group of US users.
If this test is successful, it will likely make way for other full screen ad types. Hopefully, more advertisers will be able to test them for themselves soon.