The race is now on for what brands can roll out Android 10 goodies by the end of the year, and believe it or not, Samsung might be among the first companies to do so. Far from the slowest OEM to upgrade its flagships to the previous version of Android, Samsung did keep Galaxy S9 owners waiting until the last few days of 2018. We're obviously talking about "international" units in select Asian and European regions, as US carriers took another couple of months to optimize and stabilize their own Android Pie updates.
But T-Mobile is apparently already "testing" Android 10 for the Galaxy S10 series and Note 10, which means the "Un-carrier's" official rollouts could be right around the corner. Of course, this "testing" phase could also go on for a while longer, but what's important to keep in mind here is that the updates have already moved beyond the "development" stage where the manufacturer is still "working on it."
Hence, it's possible that Samsung's work here is altogether done and now the ball is firmly in the court of the big four US carriers. If that's the case, we could see the Galaxy S10, S10+, S10e, Note 10, and Note 10+ upgraded to Android 10 in a matter of weeks in unlocked variants available across European shores, followed by major OS promotions stateside before the end of the fall.
That's obviously just an educated guess (combined with plenty of wishful thinking), so you may want to remain cautious and skeptical of everything while waiting for confirmation from Samsung and America's largest wireless service providers.