On Tuesday, February 3, it finally happened: Amazon.com (AMZN 1.67%) hit $1 trillion in market value. (It briefly touched $1 trillion in market capitalization a couple of times back in 2018 as well -- but the valuation didn't stick.)  

Before Amazon returned to the trillion-dollar club, however, something else happened: Jeff Bezos, the company's famously wealthy multi-billionaire founder, cashed out of $1.8 billion in Amazon stock.

Large pile of stacks of $100 bills

Image source: Getty Images.

Bezos's Form 4 filings with the SEC tell the tale.  

Between Friday last week and Monday this week, Bezos sold some 905,456 shares of stock at share prices ranging from just over $2,000 to more than $2,040 per share (Amazon closed today's trading just under $2,040). In total, the Amazon CEO reaped gross proceeds of more than $1.8 billion from the stock sales, which were made as part of a pre-arranged stock sale plan -- i.e. he did not sell off his shares just before Amazon hit its highest market valuation ever on purpose. These sales had been arranged to happen automatically some time in advance.

So what is Bezos doing with all this suddenly liquid cash, and why is he selling at all, if Amazon stock is going nowhere but up?

In 2017, Bezos revealed that to finance the development of at least two separate space rockets at his Blue Origin space company, and a lunar lander to boot, he is regularly selling "about $1 billion of Amazon stock a year." That doesn't necessarily mean that the past few days of stock sales will all be going to buy rocket parts, but if I were Blue Origin, I wouldn't be surprised to find there's a check already in the mail.