Oreo should also soon be available for the Xperia X Performance.
Updated 11/27/17 – Oreo is now making its way to the Xperia X Performance, too!
Sony's Xperia XZ1 and XZ1 Compact are two of the company's best phones in quite some time, and when they were announced, they were the first two phones on the market to ship with Android 8.0 Oreo out of the box. Sony's commitment to snappy updates has really been shining through lately, and this continues with the Oreo love being shared to two of the company's older handsets.
With this update, the XZ and XZs gain Oreo's app shortcuts, notification dots, smart text selection, the Autofill API, and picture-in-picture. In addition to all of Oreo's regular goodies, Sony is also including Xperia Actions and Reminders. Xperia Actions are suggested settings that your phone will show you based on your usage, and Reminders are described as "useful prompts for unfished tasks, including emails in draft and messages."
Along with all of this, Oreo also brings the latest November 2017 security patch to Xperia XZ and XZs.
The update weighs in at 1232Mb, and according to Xperia Blog, the Xperia X Performance should receive the update soon as well.