I meant Treasury Direct (I wasn't even thinking about the other plausible interpretation, oops). It's also on my list of accounts to manage because of my I-bonds, but since I only buy those once a year it's a lot less frequent than my transactions at Schwab (which I'm doing at least monthly because of RSUs anyway).

For buying at auction, https://thefinancebuff.com/treasury-bills-cd-money-market.html seems to cover all the major brokerages.