Xperia X is listed there. Anyone knows if that also includes the Compact model?

I can see several of the compact models here: https://wiki.merproject.org/wiki/Adaptations/libhybris#Sony

But e.g. not XZ1c

Only Sony devices enrolled in their Open Devices program - typically only one device per generation.

Ubuntu Touch supports way more devices https://devices.ubuntu-touch.io/

Is Sailfish running on top of Android in this case? I'm a little confused on why Android version is relevant.

Sailfish does not run on top of Android. It is a gnu/linux system with a Qt interface. It has an Android layer called AlienDalvik which runs on top of it. But it also has native apps written in C++/Qt. You can also run FlatPack apps which is interesting. I believe it uses Wayland for it's display server.

The Android apps blend pretty seamlessly with the whole experience. For example, the keyboard that pops up in Android apps is the same as the one in that pops up in native apps.

My guess is that Sailfish OS is reusing android device drivers.

It uses AOSP binary blobs published by Sony when installed on Xperias.

I don't think so, the model numbers are specified:

> Sony Xperia X Single SIM (F5121) > Sony Xperia X Dual SIM (F5122)

Get the compact model's number to check.

Libhybris is andoid dependant. There are a ton of community ports. The volla I use (gigaset gs290 also) also has ubuntu touch support. But sfos is much better. Mobian can also be installed via ubports, but i havent tried.