Hello, thank you for asking. To Trade U.S. Treasuries like T-Bills in TWS, you can:
Add the symbol “US-T” to your Watchlist or Order Entry window to open the Treasury Bond Selector and choose a T-Bill contract to add.
Right click on a blank line in your Watchlist and select “Treasury Bond Selector” to pick a T-Bill to add.
Use the predefined “U.S. Treasuries (On-the-run)” watchlist in Mosaic which includes current on-the-run T-Bills.
Once added to your Watchlist, right click and select Trade > Order Ticket to place an order. You will need bond trading permissions enabled in your account to trade T-Bills: https://www.ibkr.com/faq?id=35798322
We hope this helps!