In the Army Reserves, is it called Extended Combat Training (ECT) or Annual Training (AT) officially?

From what I have been told, ECT is a type of Annual Training. It is done when a unit is in the train up phase and about to move into the trained-ready pool, or are one of the formations that are part of Ready Force X. Otherwise, it's just Annual Training.

For example, a Construction EN unit might use (what is called) AT for some improvement mission like building structures on a training FOB, or improving Weapons Qualification Sites. But if that same unit is moving into a potential deployment pool, then they will do Extended Combat Training where they focus on AWT.

I don't have any doctrine to refer to; this is just what I have put together from working with S3 shops for most of my career.

1SG (Join to see) this is more or less correct. AT refers to the reserve obligation to perform active duty time for training.

ECT refers to specific ATs and exercises meant for a field environment designed to test if a unit is able to fulfill its METLs. This often lumps Units within a specific branch together though (Ex. Medical units).

WAREX is another exercise that is meant to incorporate a multitude of units from multiple branches into one combined exercise.

In theory (for the reserves), ECT was something done in years 3 or 4 and WAREX year 5 of the cycle. The reality is you can go multiple times in a cycle. Also, with the Sustainable Readiness Model, expect the nature of training to change over time as well.

Just call it AT, no confusion. Some folks come up with different names for UTAs, for example, Drill, Battle Assembly, etc. When you get down to it it is Unit Training Assembly. Same same for AT.

The only thing that I know of that is ECT is that electronic weapons shooting simulator. Which are usually subtasks when my unit has gone to Annual Training.

tl;dr — AT = ECT
Same, same.
AR 140-1 does NOT mention "Extended Combat Training" at all. It's not a "thing" -- it's a made up term.

The USAR transitioned from "IDT/Weekend Drills" to "Battle Assemblies" per the Chief, Army Reserve/CG USARC directive (LTG Helmly as I recall; and the directive was documented in a policy memo and/or Command Training guidance) - this to focus IDT on METL tasks. A LTC on USARC staff thought "Annual Training (AT)" should be changed to "Extended Combat Training (ECT)" (to mirror movement to use "Battle Assemblies") and put it on some slides used during collective training scheduling workshop(s). Some attending USAR MSC representatives thought the "AT" name change was official policy and started using it in their commands...some commands still use "ECT" though the official term is "Annual Training" (AR 140-1).

I’ve heard it called both.