I was shocked too (I would have guessed closer to 1-2k), so I searched around.
In early 2015 he said he just passed 2,000 paying subscribers. [1]
In an interview from February this year he didn't say anything specific about customer numbers but he did say, "Certainly I work hard, but the amount of work I’m doing today is the exact same amount of work I was doing three years ago. The only difference is my income is 100 times higher. And it’s because that $10 scales, and it scales very, very well." [2]
Of course, who knows what he was making three years ago (he was a "Growth Engineer" at Automattic then according to his LinkedIn profile, fwiw), or whether he meant "100 times" literally or just figuratively for "a lot".
But it doesn't seem unreasonable that he might have well over 10k paying subscribers.
For what it's worth, I'm a paying subscriber. I always enjoy reading his daily updates on my commute in the morning.
I've been a happy paying sub of Stratechery since October 2015, and would be glad to discover that subs have 'almost surely grown exponentially since [November 2014].' Just wondering what your basis for that assertion is? Looking at (admittedly poor) proxies like Twitter followers, Facebook fans, and estimate domain visits from various sources I don't see any sort of exponential growth...though to be fair the sources I am looking at go back to mid-2015. Again, poor proxies and would be happy to know Ben is doing this well.
