“Yes, we're adding 38 new Alstom Citadis Spirit trains to keep service frequent and smooth as the network expands.
[…]”

What’s confusing is that the train count is only listed for the eastern extension. There’s no mention of quantity for the western extension.

I doubt they will, but it’s possible they will rotate trains while 1 West and 3 are still being built.

As I recall, they started with 37 delivered with 32 being the number that needed to be contractually available at any time to run 2 car trains on initial line 1. ( so 16 trains of 2 cars). Post Covid they agreed to reduce frequencies, so number may be less, and then agreed to go down to I think 12 trains of 1 car due to the bearings.