Amazon CEO Jeff Bezos has released his latest annual shareholder letter.

In the letter, Bezos stressed the importance of having high standards in running a business. By setting high standards, companies are able to live up to "ever-rising customer expectations," he said.

"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," Bezos wrote in the letter.

Bezos also disclosed for the first time that Prime now exceeds 100 million members worldwide. In 2017 alone, Amazon added more Prime members than any prior year, and shipped over five billion items through the paid membership service worldwide, he said.

Amazon also sold the most number of devices last year, with customers buying "tens of millions" of Echo devices, Bezos wrote in the letter.

With regards to Whole Foods, Bezos said the "technical work" is currently under way to bring Prime member benefits to the grocery chain.