Alphabet officially reached a valuation of $1 trillion on Thursday, becoming only the fourth American company — and the fourth tech company in history — to reach this once unthinkable milestone.

At a closing stock price of $1,450.16 per share, the company formerly known as Google reached a market capitalization of $1T, and the only other two companies in the world worth more right now are Apple and Microsoft. As the New York Times notes, the milestone comes at a time of awkward maturing for Alphabet as a corporation, and just a little over a month after its founders decided to step back from active roles at the company.

Apple was the first company to cross the $1T threshold back in early August 2018, and Amazon briefly did so as well about five weeks later, only to have its stock price tumble back and stay below the needed stock price of $2,050.27 ever since. (Amazon closed Thursday at $1877.94.) Microsoft has stayed mostly above the mark for its $1T market cap since crossing the threshold last April at a stock price of $130.51. (Microsoft closed today at $166.17.) Both Microsoft and Amazon have seen their cloud computing businesses grow and thrive in recent years, and they're going toe to toe on that front. Microsoft also makes heaps of money, still, on its Windows and Xbox platforms, and from Office software and LinkedIn.

At Alphabet, the revenue streams are many. Google search pages have been squeezing in more ad space, and the company is making untold sums from YouTube as well, though those numbers are never broken out for investors. As the Times reported last year, Alphabet remains cagey about just how much revenue YouTube generates for the company. It's "probably" between $16 billion to $25 billion per year, which would land it in the Fortune 500 if it were its own company. Alphabet also doesn't break out user numbers, profit, or any other metrics for YouTube, though analysts still believe it doesn't generate the kind of money that search still does for the company.

Also, this one-trillion-dollar valuation day comes less than a year after Alphabet shocked Wall Street by delivering a first-quarter earnings report that was $1 billion below expectations. At the time, CFO Ruth Porat attributed the shortfall to a "deceleration" in YouTube ads, but didn't elaborate.

Some of that "deceleration" may be due to the FTC scrutiny YouTube was under all of last year pertaining to children's content and ads targeted at children. Under COPPA (the Children's Online Privacy Protection rule), tech companies aren't allowed to target children under 13 with ads, and it was found that a huge number of YouTube users are under that age — despite there being a separate YouTube Kids platform. In September, Alphabet and YouTube agreed to pay a $170 million fine to the FTC over COPPA violations, and agreed to a host of changes to how it handles children's content overall.

Previously: Google and Facebook Slip Out of Top Ten In Glassdoor Ratings By Employees