https://news.xbox.com/2017/10/23/play-three-generations-of-games-better-on-xbox-one/
Basically ~200m hours in 4 1/2 months.
Previous milestones for comparison:
June 7th 2017 - 508M hours
November 10th 2016 - 210M hours
August 18th 2016 - 145M hours
June 28th 2016 - 100M hours
We created the Xbox One Backward Compatibility program for our fans and were thrilled with the response weve seen gamers have spent more than 700M hours playing Xbox 360 games on Xbox One. Its been quite the journey; the team has worked tirelessly so you can experience your favorite games across generations on Xbox One. Original Xbox classics join more than 400 Xbox 360 games in the Xbox One Backward Compatibility program, which also means well have our largest console launch portfolio ever when Xbox One X releases on Nov. 7.
Basically ~200m hours in 4 1/2 months.
Previous milestones for comparison:
June 7th 2017 - 508M hours
November 10th 2016 - 210M hours
August 18th 2016 - 145M hours
June 28th 2016 - 100M hours