Silicon Valley’s $120 Million Campaign Puts California Billionaire Tax on Defensive

California’s proposed one-time billionaire wealth tax is losing momentum as a well-funded opposition campaign gains steam.

As of July 10, prediction market Polymarket gave the measure just a 28% chance of passing, following reports that prominent Silicon Valley technology leaders have assembled a $120 million campaign to defeat it. If those figures hold, the contest could become one of the most expensive ballot measure campaigns in California history.

Supporters say the proposal would generate billions for public programs by requiring the state’s wealthiest residents to pay a one-time tax on large fortunes. Opponents argue it would discourage investment, drive high-net-worth individuals out of California, and trigger lengthy legal challenges.

Although prediction markets are not public opinion polls, they are closely watched because they reflect how traders evaluate campaign fundraising, political developments, and the likelihood of a measure’s success.

With the November 2026 election approaching, both sides are expected to dramatically increase spending and voter outreach. The outcome could shape not only California’s tax policy but also future wealth tax proposals across the nation.

Sources:

• Polymarket, “Billionaire one-time wealth tax passes in California election 2026?” (accessed July 10, 2026).

• California Secretary of State, statewide ballot measure information.

• California Fair Political Practices Commission (FPPC), campaign finance filings and committee disclosures.