Heads up to others that IBKR has ended TPLUS1. Not sure when this happened but within the last few months. Discovered when I tried to use it yesterday against a covered call assignment and the exchange wasn't available. Called IBKR up and customer service confirmed TPLUS1 is no more after thirty minutes of TWS troubleshooting, checking exchange permissions, etc. Feel fortunate that I'm only stuck paying the tax bill on 100 shares so didn't cost me too much but it could have been very material. Super poor form on IBKR's part that this wasn't communicated to customers who have enabled TPLUS1 exchange permissions. (Correct me if I'm wrong but I searched my emails/messages and didn't find anything.)