Kernels are not typically removed ever unless you remove them. You will want to uninstall the older ones as your boot partition will fill up and halt new kernel updates.
4.18 rc7 was supposed to be the final, but they had some regression testing failed so 4.18 rc8 was releases a few days ago which is supposedly the final release of 4.18.
Unless you need it for some hardware support or you just like bleeding edge I recommend staying a few versions back or keep one or two other kernels installed in case you have issues.
@Neemobeer Q: How many kernels will Ubuntu keep until it starts deleting the older ones? I am seeing improved returns with regards to my Nvidia issue. I don't have much time to mess around ATM, as my wife will be having a surgery tomorrow. I'm a bit tense.
Kernels are not typically removed ever unless you remove them. You will want to uninstall the older ones as your boot partition will fill up and halt new kernel updates.
I do NOT intend to install it but I just got a message via UKUU that a minor kernel update 4.18.2 is available. (I plan to use only official released updated kernels in the future!) just for anyone's knowledge and info