Had my first V12.3 drive for about 30 minutes through suburban Maryland and downtown DC. Overall, very impressed. A couple of disengagements for it choosing the wrong turn lane, but I would say on the whole, it did better than V11. My only slightly concerning disengagement was at this intersection, waiting to turn left:
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Cars were backed up, so none of the turning arrows nor the short piece of double-yellow were visible. V12.3 started to go around the backup, and would have ended up on the left side of the double-yellow if I had not disengaged. But without being able to see the arrows or the double yellow, I can see how it thought that would be the left-turn lane and/or a decent space to navigate around a blockage.
Also, question for other city-drivers to ascertain whether V12.3 exhibits region-specific behavior: How good is V12 for you at not "blocking the box?" I was actually very impressed at how V12 would wait on the far side of an intersection or garage entrance if it thought it did not have room to traverse the intersection.