For its previous two 4K phones, Sony's settings defaulted to using a Full HD, not even Quad HD, resolution for everything. It only kicks the phone into 4K when the app supports it. With the Xperia 1, it flips the tables and the phone operates in 4K all the time except the app doesn't support it. This means that the entire Xperia 1 user interface and soon to be updated Sony native apps will be running in 4K. In theory, you will see crisp and clear images and text. In practice, you will most likely be rushing to charge the Xperia 1 long before the day is over. While watching a 4K video on a 6.5-inch 4K screen may be an eye-opening experience, there is still some debate whether users are even able to fully appreciated QHD resolutions for day to day regular use. That is why many phone makers stick to FHD or FHD+ screens to keep costs low. Additionally, pushing that many pixels around drains the battery faster, and the Xperia 1's meager 3,300 mAh might not be up to the task.