It looks like we have confirmation that the Xperia 1 will be rendering everything in 4K all the time:
https://www.gsmarena.com/xperia_1_screen_uses_4k_resolution_all_the_time-news-36162.php
Apps that don't support 4K resolutions will be scaled down though.
https://www.gsmarena.com/xperia_1_screen_uses_4k_resolution_all_the_time-news-36162.php
Apps that don't support 4K resolutions will be scaled down though.