The odds of California voters passing a proposed one-time Billionaire Tax have cratered on Polymarket — marking a stunning swing for the soak-the-rich measure as it fights to become a reality.

Traders on Wednesday morning gave the tax just an 18% chance of passing in the 2026 California election.

That is a sharp drop from 40% on June 11 — and a massive collapse from the market’s 61% high on Jan. 9.

The latest number also appears to put the tax bellow a previous low of 19% on Jan. 4, according to the chart on Polymarket’s website.

The prediction market, which has more than $3.38 million in volume, asks whether a “billionaire one-time wealth tax” will pass in California’s Nov. 3, 2026 election.

Under Polymarket’s rules, the market resolves “Yes” is any proposition containing a one-time wealth tax targeting individuals, households or family units with at least $1 billion in wealth, assets or net worth passes in that election. Otherwise, it resolves “No.”

The slide comes as the wealth tax becomes a high-stakes fight in the Golden State, with supporters pitching it as a way to raise money for state programs and critics warning it could drive wealthy residents and businesses out of California. Google co-founder Sergey Brin has been perhaps the most surprising opponent, breaking years of relative political silence to throw his weight, and his wallet, behind defeating the plan.

Polymarket posted on X on June 15 that the billionaire wealth tax was “no longer projected” to appear on the California ballot, though that post referred to the ballot-access market — not the market on whether the measure would ultimately pass.

The latest odds show a dramatic reversal from January, when bettors briefly fave the proposal better-than-even odds of passing.

Now, with the 2026 just months away, the market is treating the billionaire tax as a long shot.

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