I got the answer from Carl an Engineer at Trek. Turns out it is:
that's the upper headset bearing PN for all SCs, 2010-present, with the external steerer (aka bayonet style) fork. it's a custom
bearing, so I'm not sure you'll find it anywhere other than through
your Trek dealer.
1st generation SC 7-series bikes (which technically were model years 2010-2013) that had a standard stem on a 1" aluminum fork
steerer used a 1" cane creek upper bearing, PN 428420 from your Trek
I wanted to buy it online so I found it by the Cane Creek model #
The original SC7 upper headset bearing is a standard 1" threadless
headset bearing with 45deg chamfers...your Trek dealer can order PN
428420...Cane Creek PN is BAA0004K.
Ordered part BAA0004K from Amazon. That should do the trick.