Back when Blizzard released the Warlords of Draenor expansion for World of Warcraft in 2014, the number of subscribers peaked at 10 million players. This was two and a half years after last time the game had that many subscribers (2012), and four years after the all-time peak of 12 million.
With the launch of World of Warcraft: Legion, they appear to have reached a new peak, though we don't know how high the number is regarding paying players. During a livestream at PAX West, the developer said as follows:
"We knew this expansion was going to be something for the books, but reception has just blown us away. The early reviews are coming in, they're really positive. Fan reception has been phenomenal.
"Concurrency - we've had to check and triple check our numbers, because it's the highest they've been in recent memory. Several years, for sure."
When it comes to interpreting this, your guess is as good as ours. World of Warcraft will be 12 years old this November, and "several years" sounds like more than two years. Then again, the number from four years ago is approximately the same as two years ago, which leaves us with the all-time peak in 2010. Which one is it, Blizzard?