It is security patches only. To take all the other patches you do need to reboot, which is why it still has quarterly reboots. No real OS has solved this problem.

A 90% answer is better than no answer, which is what we've had for 40 years now.

Linux only requires rebooting for kernel updates, and with kpatch not even that.

Note that you can also only reboot the kernel, but keep userspace.