I would not bet the farm on that. I also have there OnePlus 6T from TMO. A10 is running on the international variant since October, but not on the TMO version.
This is very concerning. If a company doesn't have the resources to update software it should not lock phones in the first place.
I messaged TMO customer service to ask when A10 was coming last week and they told me no one outside of Korea was getting the update. They had no idea that unlocked, Verizon and Sprint were all sending it out. How pathetic is that?