https://www.recode.net/2017/10/27/16550716/stream-netflix-stranger-things-2-release-live-date-facts-stats-binge-watch-upside-down

We don't know if “Stranger Things” is Netflix's biggest hit. But “Stranger Things” feels like Netflix's biggest hit, and Netflix is certainly treating it that way: It has been promoting the show nonstop in the 15-month run-up to the new season of “Stranger Things 2,” which is now live. (Wait, don’t go check yet!)

Again, we won’t ever know if Netflix’s big marketing run-up actually worked, because the company famously doesn’t release numbers about its home-grown programming or really anything else on the streaming service. It’s pretty much a black hole for metrics.