Last we heard, Amazon Prime was reportedly sitting between 60 and 90 million subscribers, but those numbers weren't official. But now that we have this information straight from the source, we can stop trying to guess whether Amazon's renowned offering is a hit -- though who knows when the company will release these numbers again. 100 million members is quite impressive, especially when you consider that that's roughly one third of the US population. And at $99 per year, it's not exactly cheap.

On top of that, Bezos said in his letter to shareholders that Amazon Music "continues to grow fast" and it now has "tens of millions" of paid subscribers. He added that, over the past six months, membership for company's music-streaming service has more than doubled. Spotify and Apple Music, the two biggest competitors in the space, have 71 and 36 million paid listeners, respectively. Amazon Music has a long way to go to catch up to these two, but based on the vague "tens of millions" statement the company's been touting, the app doesn't appear to be a bust.

"This year marks the 20th anniversary of our first shareholder letter, and our core values and approach remain unchanged," said Bezos. "We continue to aspire to be Earth's most customer-centric company, and we recognize this to be no small or easy challenge. We know there is much we can do better, and we find tremendous energy in the many challenges and opportunities that lie ahead."