Automatic upgrade from M-Class on International long-haul flights?

I am 1K. Almost all my travel is international. My usual travel route is from IAD to BRU and then onward to points in Africa.

My strategy for trans-Atlantic flights has been to purchase a W, Q or V class ticket and then upgrade to business (if space is available) using a GPU (aka SWU).

However, I recently saw a mention about an automatic upgrade to business if I purchased a M (or higher) class ticket. Does this automatic upgrade from M-Class apply to international travel? Or, does it (as I suspect) only apply to domestic (or short-haul) travel?

If it does apply to international travel, then at what point in the purchase process would that upgrade become available?

Thanks
Baertracks