Originally Posted by SEA1K4EVR

What he says is accurate as of right now. But starting sometime in the 2nd quarter (date not certain yet) CO elites will get free E+ and free first class upgrades on UA flights. At the same time UA elites will get preferred seating and free upgrades on CO flights. UA elites do not officially get either of those things on CO right now but it's been reported that a few have gotten preferred seating and upgrades. It's just not supposed to happen until 2Q.