Sergey Brin, the Google co-founder worth an estimated $260 billion, has poured $102 million into defeating California's proposed billionaire wealth tax — a ballot measure that could leave him with a tax bill of roughly $13 billion if voters approve it in November.
What Is Proposition 40?
Proposition 40, on California's November 3, 2026 ballot, would impose a one-time 5% tax on the net assets of state residents worth more than $1 billion — about 200 to 250 people. The tax would apply to those who lived in California at the beginning of 2026 and could be paid in five annual installments starting with the April 2027 tax return. Real estate and retirement accounts would be excluded.
Supporters project the measure would raise around $100 billion over five years, with 90% going to the state's healthcare program and the remaining 10% to education, food assistance, and administration. They frame it as a counter to federal funding cuts to public programs.
Brin's $102 Million Bet
According to campaign filings, Brin donated the $102 million to Building a Better California, the political advocacy group leading the opposition. That makes the 53-year-old former Alphabet president the largest individual donor fighting the measure — contributing more than half of the $187 million the opposition has raised. Groups supporting the tax have raised roughly $32 million.
The math explains the spending: at a net worth of about $260–270 billion, a 5% levy would cost Brin somewhere between $13 billion and $14 billion. In those terms, $102 million to defeat it looks like, as CNN put it, one of his best investments.
Brin has tied his opposition to personal history. "I fled socialism with my family in 1979 and know the devastating, oppressive society it created in the Soviet Union. I don't want California to end up in the same place," he told the New York Times in April.
Billionaires Split — and Politicians Pick Sides
Brin isn't alone. Other major donors to the anti-tax campaign include Kleiner Perkins chairman John Doerr ($30 million), former Google CEO Eric Schmidt ($27 million), venture capitalist Peter Thiel, and Stripe CEO Patrick Collison. Tech leaders have threatened to move their residences — even their businesses — out of California if the measure passes.
Not every billionaire agrees. Nvidia CEO Jensen Huang shrugged off the proposal: "We chose to live in Silicon Valley, and whatever taxes they would like to apply, so be it. I'm perfectly fine with it."
The politics are scrambled. Governor Gavin Newsom — widely expected to run for president in 2028 — says he will vote no, calling it a "poorly written state measure." Both gubernatorial candidates, Democrat Xavier Becerra and Republican Steve Hilton, also oppose it. An August UC Berkeley-IGS poll found 48% of likely voters in support and 41% opposed — far from a done deal.
What Happens Next
California election law adds a twist: two competing measures, Propositions 41 and 42, could negate Prop 40 entirely if they pass with more votes. And skeptics cite a Stanford Hoover Institution analysis estimating the tax would collect only about $40 billion — less than half of supporters' projections — as billionaire departures have already removed over $550 billion from the potential tax base.
With nearly $100 million in opposition ads already reserved, the fight over Proposition 40 is shaping up as one of the most expensive political battles in American history — and its outcome will be decided by California voters this November.
Watch: Google co-founder Sergey Brin enters California billionaire tax fight — a video report on Brin's $102 million campaign against Proposition 40.