Amazon has never been open about the number of people who subscribe to its Prime service, but in Jeff Bezos' latest annual shareholder letter, the CEO spelled out just how many members it now boasts: over 100 million globally.

Up until now, it's been left to analysts and market research firms to estimate Prime subscriber figures, with companies putting the number somewhere between 60 million and 90 million last year. In 2013, Amazon did give a very vague Prime statistic, saying that it had "tens of millions" of members. Now, we know that 13 years after the service launched, a massive 100 million people feel the annual or monthly fee is worth it for the fast, free shipping, access to streaming videos and music, and more.

Bezos added that last year was a record for Amazon, as more people joined Prime than any previous year, including 4 million in a week in late 2017. Additionally, the company shipped more than five billion items with Prime worldwide. Launching Prime in new locations such as the Netherlands, Mexico, and Singapore will have contributed to those massively successful 12 months.

Amazon has in the past faced criticism for allegedly pushing some employees to breaking point and allowing a toxic working environment, but that might be the price for what Bezos calls high standards.

"How do you stay ahead of ever-rising customer expectations? There's no single way to do it - it's a combination of many things. But high standards (widely deployed and at all levels of detail) are certainly a big part of it," the CEO wrote in the letter.

"So, the four elements of high standards as we see it: they are teachable, they are domain specific, you must recognize them, and you must explicitly coach realistic scope. Building a culture of high standards is well worth the effort, and there are many benefits."

With Amazon's quarterly earnings report set to be announced on April 26, expect to learn more details about the state of the company next week.