When do I find out if I am an 11B or 11C during OSUT?

I found out day 1 right off the cattle cars. Our Drill SGT told us what we were going to be doing

You are separated at the beginning of basic training now. You should be told while you're going through in processing at 30th AG, but without a doubt you will know when you get to your basic training company. There are specific companies on sand hill responsible for mortars, I don't know which one's specifically off the top of my head though.

During the second part of OSUT what was AIT. They will start splitting you apart for Mortar classes