Both apps now support uploading images in 4K. This likely refers to the same 4096x4096 resolution limit that exists when uploading from Twitter web. We’re testing ways for you to upload and view 4K images on Android and iOS. To check the new feature, I uploaded a 4096x4096 image twice from the iOS app with and without 4K quality enabled and once through Twitter web. The 4K mode reduced the file size by compressing it but the 4K resolution was maintained.

Source: The Nation March 10, 2021 21:00 UTC