I'm flying J from IAD to LAX on a 772. Config now is showing new Polaris. I've been checking seat maps for the flights scheduled back and forth between IAD and LAX over the past few days and they have all changed to the old 3-class united configuration (8F/40J...) I'm guessing that mine will also be switched based on that. What I'd like to know is how will I get reassigned? Also, it seems like united considers the 8F and the 40J seats to be the same, so what are the chances of me getting one of those 8 seats?

Random (in my experience). I think they might try to keep it similar (aisle -> aisle), but i've gone from an aisle to smack in the middle of one of those 8 seats.

Check often. If you happen to get a text of an aircraft swap, check and select ASAP.

FWIW, I just flew MUC-IAD and got switched from a Polarized 772 to a 3 class IPTE one about 3 days out. Everybody seems to have been auto reassigned (no empty seats right after the switch) and I got reassigned from 9G (middle aisle) to 9C (middle aisle).

This suggests that they try to keep you in the same location, which implies that Rows 1-2 might get moved to the old F seats. But I'm just one very inconclusive data point.

Thanks for the info! I've been obsessively checking so I hope to catch it early and not get stuck in the middle of the 8!

I'm 11 D & G right now in Polaris so I'm worried that if the switch happens I'll end up in the middle in the back if your logic holds up

Does anyone know how they work the reseating? Do they just put me in 8D on the new plane, or do they just let everyone pick their new seat when we check in or realize that there was a switch?
I too have been watching like a hawk. I see 9A still open on old config on my flight and that would be preferred over 8D on the new config.

UA doesn�t care. I�ve experienced a variation of preferential reseating versus random reseating as a 1K when aircrafts are swapped. Keep watching like a hawk as UA will happily reaccommodate elites into preferential, open seats.

IME, they assign you to a new seat. Seem to try and match window / aisle to window / aisle, but not sure about anything else.
Watching like a hawk is the best strategy.

I was watching it. Last night it hit the flight status page as it was 2-2-2. This morning I was moved to 8L in the new configuration but was able to grab 9L due to the light load. Still 10 empty on Tuesday the 7th.

Nice. I am now watching for my return, NRT->ORD, as it is showing the 3 cabin config still.
Would be fun to ride in a GF seat one last time.

I noticed United starting sending emails notifying of a switch into the GF cabin. The headline is "We've moved you to a better seat for your flight to xxxx".

This week I received that email and got a prime 2K seat, and then noticed a day later that I was switched to an old C class sardine seat. As far as I'm aware, there was never a swap back and forth between aircraft that would justify reshuffling to any degree let alone a downgrade, but perhaps. I called the GS line and asked about the seat change and what they could do to get me back into GF and it turned into an awkward/tense discussion where no movement was made on their end...
"Sir, the same service is provided throughout both cabins."
"Yes, I know that, but the seat is much better in the former GF cabin"
"Sir, what is considered a 'better' seat is very much a subjective matter"
"Oh come on, the email from United literally says 'we've moved you to a better seat'. I think we all know what is the better seat here."

She had no clue this email was being sent by United. When I forwarded this evidence of my prior seat selection to the GS email address, they said there was nothing they could do about future reservations, only past customer service issues. I said, well now it's a customer service issue because I've been downgraded. Silence. Ugh. GS service is going downhill.

In your flight to Shanghai

2A in the pmCO configuration got mapped to 2A in the Polaris configuration. Managed to snag 5A, which was previously occupied in the pmCO configuration, though I suspect it was a couple in 5AB who got moved to 5DG or one of the other paired seats, thus freeing up 5A. FWIW, 5L, which doesn't exist in the pmCO configuration, was also available in the Polaris configuration.

This was me last week. ORD-NRT was showing 3 class up until T-17 and had managed to snag 3 of the old GF seats. Then at T-16, BAM!, the old switcheroo into a Polarized 772 with our 5 seats scattered all over the main J cabin.

Flying AMS to ORD on the 12th. Seat layout is for 2-1-2 on a 763. However in the Ammenities section it says business is a 1-1-1 layout.

When I look up the info on the plane it says it is Fleet Number 6456 which is a new polaris equipped aircraft. Does this mean that the seatmap will switch over to a true polaris seat map in the next few days?

Wow, that's pretty bad. If I am reading the fleet update page correctly, looks like they are right at 50% of the conversions completed. Luck of the draw, I guess...