I can confirm it as well. The other day I had a typical long multi-leg scheduled day and I usually use the flight status option on the UAL app to track my flights to know about delays ahead of time to save leaving the hotel/home any earlier than needed. The night prior I received notice that all of my flights had canceled. On a forecasted blue sky day. So I went in to the app and saw that UA added back the same flight numbers and city pairs but operated by another UAX carrier. So the flights went just not on us. Minutes later Crew Scheduling called with a reroute for me. Spoke with another CA and FO that next day that have had this happen too. Seems like it’s a very recent thing. Can UAX carriers “trade/add/drop” with each other similar to us?