I didn’t realize that while Sabayon is a rolling distribution, the kernel needs to be manually updated (disturbingly, more and more of my knowledge seems to be coming from reddit…).
I decided to update my kernel today because suspend has never worked on my T420 and I figured a kernel upgrade would do the trick.
It actually wasn’t too bad. Sabayon has a built-in kernel upgrade tool. Details on it can be found here. This post has the easiest-to-understand (for me) command syntax: kernel-switcher switch sys-kernel/linux-sabayon-3.0-r10.
I ran the update, checked everything, and it worked. And now I can suspend!
I’m not sure I’ll ever upgrade the kernel again.