I recently purchased X1 C6; I am back to Thinkpad after 8 years of digression to Macbook. I will probably write a post explaining why I switched back, but for now I will focus on my story of getting S3 sleep with it under Ubuntu.
One thing I really miss from Macbook is how easy it was to simply close the lid and not worry about draining the battery. Unfortunately, with X1 C6, that is not the case. With Windows 10, closing the lid makes it go to Si03 sleep state where some processes can be on doing stuff in the background. The idea is great, but unfortunately in real world this new Si03 sleep state simply drains the battery so much that I just want to go back to old S3 state, where none of the processes can be on.
Since I installed Ubuntu on this machine and will mainly use Ubuntu, I searched for methods to enable S3 sleep rather than stupid Si03 sleep. After spending much time, I finally found a solution, and I want to share it with anyone who needs this.
At first, I tried this post, but did not work. Then, it was this answer here by Adonis that saved me. Basically, the missing step was to to generate grub.cfg file from grub-mkconfig from /etc/default/grub and then add initrd /boot/acpi_override.
Before this patch, it didn't even last a full day on sleep. Now with this patch, it seems to drain 10% a day in sleep. This is not as good as Macbook, which lasts about 30 days in sleep, so about 3% per day, but I guess this is better than 100% drain per day. With Windows, it was about 30% drain per day in sleep.
I really like this laptop, but I have to admit that I miss Macbook when it comes to this sort of minute convenience.
By the way, I really appreciate that people managed to create this patch and shared with all of us. I really respect their knowledge and skills. This was something Lenovo engineers could not even do!