[dominicperry]

This used to be relatively simple for Carbon.

Carbon used to come with a standard PT perpetual license with one year of support+upgrades. If you do nothing after a year, the license remains perpetual and you are stuck at the last version you had access to. The alternative is to pay for a year of support and upgrades - about £200 / $200 per year. There is no option or need to move to a subscription license.

The confusion used to be that if you already had a standard perpetual PT license before you purchased the Carbon, you could INSTEAD choose to extend the support+upgrades on your existing perpetual license for one year.

Now is it substantially more confusing, because many/most people who bought a Carbon get a Perpetual ULTIMATE PT license as well. Yes - you get BOTH standard and ultimate, both with support+upgrades for a year. At the end, you have to decide to:
1) do nothing, in which case you keep both perpetual licenses, stuck at the final version.
2) add (pay for) support and upgrades on Standard PT
3) add (pay for) support and upgrades on Ultimate PT
4) add (pay for) support and upgrades on BOTH Standard and Ultimate.

At no point is there any real sense in moving to a subscription if you have a Carbon.

You should be able to see all you options inside your Avid account, although PT standard and PT ultimate are in different places - and in my case they have different dates because I received the PT Ultimate as a "gift" from Avid when they started the Ultimate promotion with Carbons, some time after I'd purchased the hardware.

DO NOT let it expire, unless you have already bought a reinstatement or are sure you can buy one from a reseller - be certain they have stock. All Avid reinstatements were withdrawn a year or two ago, and then unexpectedly brought back for ONLY December this year.
(by all means let it expire if you just want to go to a Perpetual with no support, but don't assume that reinstatements will be available again).

Dominic