It feels like a long time coming, but Twitter finally allows its mobile users to tweet and view pictures in 4K. Its web app already supports higher-resolution images (up to 4,096 x 4,096), but Android and iOS users were limited to half of that resolution before this update.
To use this new feature, you will need to go to the "Data usage" section of the settings menu in the app. You will need to enable both "high-quality images" (for viewing) and "high-quality image uploads" (for tweeting). You can select whether you'd see or upload these images on cellular and Wi-Fi, just Wi-Fi, or disabled entirely.