04-26-2018 09:19 AM
According to the (always fantastic) Arch wiki, setting the acpi.ec_no_wakeup kernel param will enable Si03 sleep. I'd refer you there for more information. Keep in mind, this might be tied to a specific kernel version. Overall, the Arch wiki seems to have some of the most up-to-date information on the X1C6 and Linux. Some of it may or may not apply to your distribution.
04-26-2018 09:37 AM
S0i3 is mostly working on the X1C6 (haven't tested) and the X1Y3 (have tested). Just make sure to disable the card reader in the bios or via the command line as described on the archwiki linked above. If you don't do that, you will likely lose 3-5% battery per hour in S0i3 sleep.
As an FYI to any other X1Y3 owner reading this, a few other usb devices need to be disabled (in addition to the card reader) to have an acceptable power drain in S0i3.
04-26-2018 09:41 AM
04-26-2018 09:50 AM
If you have the X1C6, I think that is the only thing to worry about from what I've read.
On the X1Y3, it seems the WACOM tablet and (1-10) and another unidentified usb device (1-9) need to be disabled. Otherwise, there is too much battery drain (even with the card reader disabled in the bios). There are no bios settings for these two.