Meta's tax rate hit 2% on an $8 billion Treasury break. Senators want answers by Halloween.

Meta paid an effective tax rate of 2% on $53.5 billion of pretax income for the first nine months of 2026, down from the 21% federal statutory rate, and an $8.03 billion Treasury decision explains most of the gap. "Our effective tax rate for the nine months ended September 30, 2026 was 2%," Meta said in its quarterly report filed this week. The company's tax provision came to $1.03 billion.

The mechanism sits in a single regulatory action. On Feb. 18, Treasury issued Notice 2026-7, granting relief from the corporate alternative minimum tax on previously capitalized U.S. research and development costs. Meta recognized an $8.03 billion tax benefit in the first quarter as a result. That benefit partially offset a $15.93 billion charge Meta booked in the third quarter of 2025, after the One Big Beautiful Bill Act became law — a quarter in which Meta's effective rate hit 87%.

How much did the Treasury notice change?

The notice moved Meta's numbers by wide margins. The company reported a first-quarter 2026 rate of negative 23%. Without the Treasury benefit, that rate would have been 37 percentage points higher, about 14%. Meta's first-quarter report says the rate fell "primarily due to Treasury Notice 2026-7."

For the full nine months, a Fortune calculation based on Meta's filings puts the tax provision at about $9.06 billion without the benefit — roughly 17% of pretax income. The third-quarter rate, which the notice did not affect, was 24%; Meta says it would have been 17% excluding a $9.89 billion charge. Absent changes to its tax landscape, Meta expects its fourth-quarter 2026 rate to land between 15% and 17%.

Why do senators want answers by Oct. 31?

A separate tax break has drawn congressional scrutiny. Citing a New York Times report from Sept. 30, seven Senate Democrats wrote to Mark Zuckerberg on Oct. 13 demanding a response by Halloween on how Meta classified its data centers as experimental to claim the federal research and experimentation credit.

The signatories: Ron Wyden of Oregon, Sheldon Whitehouse of Rhode Island, Elizabeth Warren of Massachusetts, Catherine Cortez Masto of Nevada, Maggie Hassan of New Hampshire, Ben Ray Luján of New Mexico, and Peter Welch of Vermont.

Their letter says Meta told the IRS in federal filings that its AI data centers are experimental "pilot models" qualifying for the credit. Meta's regulatory filings show the credit cut its federal income tax liability by $6.6 billion from 2023 through 2025:

• $700 million in 2023
• $2 billion in 2024
• Nearly $4 billion in 2025

"The federal research credit can be a useful and necessary tool to support our nation's innovation economy and cutting-edge research," the senators wrote. "Subsidizing your A.I. data center build is not close to meeting this standard." They asked Meta to disclose how much of its credit each year went to microchips, computing equipment, and other data center materials.

Warren extended the argument beyond taxes. "AI companies are delivering a one-two punch to families, forcing Americans to subsidize their data centers with your tax dollars and higher utility bills," she told Fortune. "We need to crack down on these Big Tech companies and make sure they pay their fair share."

What does Meta say?

Meta defends the credit claims. "Meta is one of the largest investors in research and development in the United States," a company spokesperson told Fortune. "Over the last five years, Meta invested $200 billion in R&D—$57 billion in the last year alone, advancing frontier research, building new technology, and supporting American jobs."

The spokesperson added: "Unlike traditional data centers, AI-optimized data centers are inherently new and require extensive testing and experimentation that cannot be simulated in order to get the design and build right. This is precisely the kind of domestic investment Congress encouraged when it established these tax incentives decades ago."

How much of the savings is still in dispute?

Meta's own filings show the scale of unresolved tax positions. Gross unrecognized tax benefits — savings claimed but not yet final — reached $20.82 billion as of Sept. 30, up from $16.45 billion at the end of 2025. If realized, they would cut Meta's tax provision by $14.58 billion. Meta's annual report says these benefits were "primarily accrued for the uncertainties with our research tax credits and transfer pricing" with its foreign subsidiaries.

The filings this week also detailed a new class of non-voting stock that would let Zuckerberg raise cash without giving up control, including enough to cover a potential California wealth tax. Meta says management forecasts "showed the Company's need to raise hundreds of billions of dollars over a period of several years beginning as early as fall 2026," according to its information statement.

Meta says it believes its accrual is adequate and expects to keep accruing for recurring tax positions. With the Senate deadline set for Oct. 31, the company must now explain, line by line, where its research credits went.