As being a UA 1K for the past three years, I feel quite fortunate having been upgraded operationally or with confirmed upgrades on every single transoceanic flight. Even with upgrades, I often got seat assignments with my next seat empty! The concierges and FAs have always been very accommodating, though there have been several noteworthy exceptions. On domestic transcon flights, I often get my favorite single seat with more recline and much more legspace in 767s. Only time I did not get upgraded was on a couple of domestic flights during this past summer of chaos.

With respect to CO, where I am a Platinum,
I get upgraded 100% in North America. Internationally too, I have always been able to upgrade using miles. ( CO does not offer international upgrade certificates. )

What is also exceptional about the very top-tier status is that when redeeming award trips, it sure makes a lot of difference.

I am trying to become AA Platinum by the end of the year and am looking forward to see what AA's elite status is going to be like.

I have been very careful in arranging my trips this year in order to achieve top-elite status on these three carriers. As much as I travel, I need to sit in front and rest well while in the air, as not all of my trips will be full-fare business class.