If you do a imgadm avail you will see that the latest LTS image of smartos is :

800db35c-5408-11eb-9792-872f658e7911  minimal-64-lts   20.4.0 smartos zone-dataset  2021-01-11
1d05e788-5409-11eb-b12f-037bd7fee4ee  base-64-lts   20.4.0 smartos zone-dataset  2021-01-11
188ee9ce-540a-11eb-9cc1-2748cd10e5e2  pkgbuild-lts   20.4.0 smartos zone-dataset  2021-01-11

I was wondering what happened to the rest of the images? We used to see them every quarter. Jonathan Perkin answered the question on the mailinglist (https://smartos.topicbox.com/groups/smartos-discuss/Tf17bc027dd6f9cba-M7dedf357e2bb4ca48d8065a5):

I stopped producing the non-LTS quarterly releases.  They weren't all 
that useful (in my opinion), as users are better served running either 
LTS if they want a static set of packages with the occasional security 
fix, or trunk if they just want the latest and most secure software.  

It's also hard to justify spending time and resources on them now that 
JPC is no more (so my available hardware is significantly reduced) and 
I'm no longer working on pkgsrc full-time.

Simply change your pkgin repo to the trunk version if you want the latest and greatest:

edit /opt/local/etc/pkgin/repositories.conf and replace the :

/packages/SmartOS/2020Q4/x86_64/All -> /packages/SmartOS/trunk/x86_64/All

and run a pkgin upgrade