Ran into this on a trip from YVR we just finished. When I booked it last summer, it was LH49x flight, operated by LH. Sometime in late Oct, I noticed LH had switched it to 4Y. There was no notification and unfortunately by the time I discovered this, it was too late to cancel/switch to a different carrier as the tickets had become much more expensive.

As United *G (and I believe it’s the same for AC elites), I did get benefits such as lounge access, priority boarding, fast lane, etc. so can’t complain much there. The onboard product is OK as well.

Negatives on our trip (in random order):
- 4Y charges you for pillows, blankets. What the hell?
- Didn’t have my special meal that was requested via LH. Their only response was “You order through LH? We are 4Y and don’t have it”
- An 8 hour delay on the outbound. Probably an hour was due to weather, rest was 4Y consistently running late the whole week prior
- Delayed luggage that we are still waiting to get back 3 weeks after our trip. Apparently the 4Y tag fell off, they had also reused the baggage tag number so there was some confusion due to it, etc.
- The toilets were a mess on both flights. No toilet paper, no cleaning at all throughout the flight. Quite disgusting..
- Even though LH and 4Y are supposedly in the same group, their systems just don’t talk to each other. LH was unaware of the delays, 4Y didn’t get the meal info, they kept losing my *G number, etc.

Overall, I’d probably pass on 4Y next time around as we didn’t have the best experience, but if the ticket price is really attractive and you don’t mind the types of issues we ran into, it might be ok.

Safe travels.