When you're worth $235 billion, writing a billion-dollar check looks a little different. Sergey Brin, the Google co-founder who helped build one of the world's most valuable companies, just transferred more than $1.1 billion in Alphabet Inc. (GOOGL) (GOOG) stock to charitable causes, according to a regulatory filing disclosed Friday.

Where the Money's Going

The bulk of the donation—about $1 billion—went to Catalyst4, a nonprofit Brin established in 2021 to tackle two massive challenges: central nervous system diseases and climate change solutions. A spokesperson for Brin's family office confirmed the details to Bloomberg.

Interestingly, Brin initially funded Catalyst4 by selling off $366 million in Tesla Inc. (TSLA) shares. This time around, he's sticking with what he knows best—Alphabet stock.

The SEC filing reveals that Brin transferred more than 3.5 million Alphabet shares total, split evenly between 1,778,650 shares of Class A Common Stock and 1,778,650 shares of Class C Capital Stock. While the filing doesn't spell out every recipient, Bloomberg reports that roughly $90 million went to Brin's family foundation and another $45 million to the Michael J. Fox Foundation, which funds Parkinson's disease research.

Not His First Billion-Dollar Gift This Year

This isn't even Brin's biggest philanthropic move of 2025. Earlier this year, he donated $700 million worth of Alphabet shares to the same trio of charities. That donation came shortly after Brin emerged from retirement in May to dive into work on Gemini, Alphabet's flagship AI project.

Brin's net worth currently sits at $235 billion, making him the fourth richest person on the planet. That figure has climbed by $76.9 billion this year alone—meaning he can afford to be generous and still end up far richer than when the year started.

Alphabet's Impressive Run

The timing of these stock gifts coincides with a remarkable period for Alphabet. The company's shares have jumped 67.93% year-to-date and an eye-popping 85.08% over the past six months, fueled largely by investor enthusiasm around the tech giant's artificial intelligence ambitions.

Over the past year, Alphabet's stock has traded in a range between $142.66 and $328.67. The company now commands a market capitalization of $3.87 trillion, cementing its position as one of the most valuable companies in the world. According to market data, Alphabet stock currently holds a Quality score of 87.95.

For Brin, giving away stock that's appreciated this dramatically creates a win-win scenario: his charities receive assets worth considerably more than they would have a year ago, and he likely avoids capital gains taxes on the appreciation. It's philanthropy, but it's also smart tax planning when you're sitting on billions in unrealized gains.