A Google co-founder is spending $100 million to defeat California’s wealth tax. It could become one of his best investments

By David Wright, Clare Duffy, CNN

(CNN) — Google co-founder Sergey Brin has funneled just over $100 million to a group trying to defeat a one-time state tax on California’s billionaires this November.

That seems like a lot of money, except Brin’s net worth – estimated around $270 billion, top five globally, according to Bloomberg’s billionaires index – means he’d face a nearly $14 billion hit under the tax, which proposes a 5% charge on the total assets of state residents with a net worth over $1 billion.

In those terms, $102 million for a chance to avoid the trouble seems like a decent investment ahead of California voters heading to the polls in November.

The battle over Proposition 40 has become one of the most expensive political fights in the country. Groups opposed to the measure have spent nearly $100 million on ads to reach voters, with most of their funding coming from Brin and other billionaires who oppose the tax.

The efforts from Brin and other Silicon Valley leaders are just the latest sign of escalating political activity from a new generation of megadonors, who have begun to deploy fortunes minted over the tech boom of the last two decades in attempts to shape public policy.

The wealth tax’s ultimate fate could affect the political fortunes of California Gov. Gavin Newsom, who is widely expected to launch a 2028 presidential bid and has publicly said he’ll vote no on Prop 40, and whoever succeeds him – with the two candidates in the race, Democrat Xavier Becerra and Republican Steve Hilton, scheduled to participate in CNN’s gubernatorial debate Wednesday night, also having expressed opposition.

Tech and corporate leaders have threatened to move their residences, and even their businesses, out of California if the measure passes – potentially depriving the state of crucial jobs. Proponents, however, say the tax would be a critical counter to federal funding cuts to public programs.

The outcome of the referendum could also ripple across the remaining 49 states. There’s growing bipartisan backlash to tech and billionaires from an American public concerned about data centers, AI job losses and wealth inequality, who could see the tax as a model to try elsewhere. But red and blue states alike could also be interested in making a pitch for industry titans to relocate there if the measure passes, despite that growing tech animus.

Alphabet, Google’s parent company, did not respond to a request for comment from Brin, who sits on Alphabet’s board and has become central to the company’s AI efforts.

What the tax would do

If approved, Prop 40 would allow the state to collect a one-time 5% tax on taxpayers and trusts valued at $1 billion or above. It would affect anyone living in the state as of the start of this year to prevent the wealthiest Californians from moving to avoid the tax.

“It’s too late to leave now,” said Emmanuel Saez, a professor at the University of California, Berkeley, and a key architect of the tax. “Because the ballot was announced in late November 2025, it left only one month for billionaires to leave. And we chose that design because we believe, based on the tax experts, that it’s basically impossible to sever residency with California within one month.”

Proponents say it’s a necessary response to federal health care spending cuts from the One Big Beautiful Bill Act, which they estimate leaves a shortfall of about $20 billion per year for California moving forward, threatening the state’s Medi-Cal program. They estimate the wealth tax could raise $100 billion, enough to cover the shortfall for about five years.

“Providers in places with vulnerable populations that depend a lot on Medicaid are going to be hit especially hard,” said Brian Galle, another professor at UC Berkeley who helped draft the language for Prop 40.

Polling on the tax suggests a potentially close vote. A UC Berkeley IGS poll last month found 48% of likely voters in favor, and 41% opposed. Another poll from the Public Policy Institute of California this month found that 52% of likely voters would vote yes on Prop 40 after reading the ballot title and label.

While labor unions and progressive organizers push for the measure – which advocates note would target a total of just over 250 individuals with net worths over $1 billion – there are some powerful opponents.

Newsom explained his opposition in a Substack post after the initiative made the ballot, sympathizing with its creators but advocating instead for “a true minimum tax on billionaires” at the national level. He also noted that Prop 40 would not address other state budget needs like housing, childcare or education.

“We can’t let a single advocacy organization, however well-intentioned, write the state’s tax code on its own terms,” he wrote.

The opposition

Opponents of the measure argue it could harm the state where they built their businesses and fortunes. Brin, who was born in Moscow, compared the tax in a rare comment to The New York Times to the society he fled as a child.

“I fled socialism with my family in 1979 and know the devastating, oppressive society it created in the Soviet Union,” he said. “I don’t want California to end up in the same place.”

He has emerged as one of the largest financial backers of the effort to block the tax.

According to state campaign finance records, he donated $102 million over the last year to the group Building a Better California, which has booked more than $50 million in ad time per AdImpact data.

The group is supporting a pair of rival initiatives, Proposition 41 and Proposition 42, that would limit the scope of new state taxes. If either measure passes and receives more votes than Prop 40, it could supersede the wealth tax. Building a Better California also says it supports measures to expand access to affordable housing in the state — at a time when the AI boom has contributed to surging housing costs in the San Francisco area.

Building a Better California is also among the top funders of the main “No” committee opposing Prop 40.

A cohort of other wealthy Californians also shelled out millions in the effort to block the tax, including venture capitalist Peter Thiel; John Doerr, chairman of the venture capital firm Kleiner Perkins; and Patrick Collison, CEO of the digital financial services company Stripe, according to campaign finance records.

That financial firepower has enabled the coalition against the wealth tax to reserve nearly $100 million worth of ad time this year, according to AdImpact data, against only about $100,000 in ad support in favor of the tax. Proponents have also spent several hundreds of thousands of dollars on get-out-the-vote efforts and campaign literature, according to Meghan Finegan, a representative for the “Yes” campaign.

With their airtime, opponents are running waves of ads urging voters to reject the tax, using a variety of arguments. Some ads, appealing to blue California’s broadly liberal electorate, note that Planned Parenthood and several non-healthcare unions oppose the wealth tax.

The bill targets California’s billionaires’ assets (with some exceptions) rather than just their incomes, given that many in Silicon Valley opt to take minimal salaries and maintain most of their wealth in the form of stocks, property and other assets. That could subject them to intrusive probing of their assets and encourage wealthy business leaders to leave the state, said Robert Lapsley, president of the California Business Roundtable.

“We already have all the highest taxes in the country — gas taxes, income taxes,” Lapsley said. “To create and implement an asset tax on top of that is going to drive, and is driving, the job creators that we have in this state out of here.”

Brin’s spending on the wealth tax marks the latest example of his rightward shift in both political engagement and spending — a move that other prominent tech leaders have also made in recent years as Republicans largely champion a more hands-off approach to tech regulation.

During Trump’s first administration, Brin protested the president’s travel ban on immigrants from several Muslim-majority countries, noting his own experience as an immigrant.

But there’s been a notable pivot since Trump’s reelection: Brin attended Trump’s second inauguration, dined with other tech leaders at the White House during the current administration and last year donated hundreds of thousands of dollars to the Republican National Committee. While he initially backed a pro-tech Democratic candidate in California’s gubernatorial primary this year, he also threw his financial support behind Hilton, a Trump-backed Republican.

Leaders like Brin “continue to see themselves as outsiders, young guns who aren’t part of the system,” who hope they can convince Californians that they’re all on the same side building for the future and to oppose the wealth tax, said University of Washington historian Margaret O’Mara, who tracks the tech industry. But Silicon Valley leaders’ longtime techno-optimist values are running up against an American public that is increasingly skeptical of tech’s influence on their lives.

Saez, one of the architects of the tax, also sees the fight having a broad impact.

“Prop 40 is going to be, if it passes, I see it as this historical turning point,” he said, adding that the tax could become a model for other states, “the first time when democracy succeeds in fighting back against billionaires.”

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