For anyone sitting on tens of millions of dollars in company stock, diversification has always come with a brutal price tag: the capital gains tax.
Sell off your early Nvidia, Apple, or founder shares to buy an index fund, and federal and state tax authorities will gladly take 30% to 40% of the upside off the top.
Over the last few years, though, high-end wealth advisers and boutique Wall Street shops discovered what looked like an unbeatable cheat code: bespoke exchange-traded funds built around Section 351 of the tax code. By packaging an investor’s concentrated stock into a brand-new custom ETF and quickly swapping it out behind the scenes, wealthy families could wash away their single-stock risk without writing a check to the government.Now, federal regulators are pulling the plug.
The U.S. Treasury Department and the Internal Revenue Service just dropped formal guidance—anchored by Revenue Ruling 2026-20 and Notice 2026-62—aimed squarely at shutting down these tailored diversification maneuvers. The government’s verdict was blunt: using an ETF as a tax-free vehicle to swap concentrated stock for a diversified portfolio violates federal law, and the IRS intends to challenge these deals under existing statutes.
How the Magic Trick Worked
To understand the crackdown, you have to look at the loophole planners exploited.
Decades ago, Congress wrote Section 351 of the tax code to help entrepreneurs. It allows people to transfer assets into a newly formed corporation without immediately triggering taxes, on the logic that you shouldn't be penalized simply for incorporating a business.
Boutique fund creators figured out that you could apply this same principle to exchange-traded funds.
Here was the playbook:
The Seed: An ultra-wealthy investor (or a small syndicate) transfers a massive block of low-basis, highly appreciated stock into a newly created ETF in exchange for shares in the fund. Under Section 351, that handoff was treated as a tax-deferred contribution.
The Behind-the-Scenes Swap: Once the ETF was up and running, the fund manager worked with an authorized participant (a specialized institutional market maker). The fund issued shares to the market maker in exchange for a diversified basket of securities, then quickly redeemed those shares by handing over the original, concentrated stock. Thanks to regular ETF tax rules, that in-kind exchange didn't trigger corporate-level capital gains.
The Clean Exit: When the dust settled, the original investor held shares of a diversified, market-tracking fund, having neatly shed their concentrated risk while deferring the capital gains tax indefinitely.
Because standing up a private or bespoke ETF comes with anywhere from $200,000 to $300,000 in upfront legal, filing, and administrative fees, this wasn't an everyday retail trick. It was a game strictly for family offices, founders, and executives sitting on at least $25 million to $100 million in unrealized gains. Over 120 custom funds used variations of this blueprint to absorb roughly $22 billion in assets.
The IRS Calls Bluff on the "Conduit"
What caught the eye of tax regulators wasn't the traditional ETF structure, which millions of everyday investors rely on for tax efficiency. It was the transparent intent and rapid speed of the swaps.
In its ruling, the IRS applied the long-standing "substance-over-form" and "step-transaction" doctrines. Essentially, tax authorities look past the clever paperwork to see what actually happened.
The IRS concluded that the ETF was acting as a glorified "conduit"—an artificial middleman created solely to disguise a taxable swap between the investor and the market maker. When someone deposits stock A and ends up holding diversified portfolio B just weeks or months later, that isn't a long-term business investment. It’s an asset sale, plain and simple.
Under Revenue Ruling 2026-20, the IRS decided these transactions must be treated as fully taxable exchanges under Section 1001.
The Chill Across Wealth Desks
The fallout was immediate across the private wealth sector.
Critically, the IRS issued the ruling without a grace period or grandfather clause. That means the tax agency can retroactively audit and challenge completed conversions, exposing participants to unexpected back taxes, interest, and penalties.
Legitimate conversions—such as when an investment manager rolls an existing, diversified separately managed account (SMA) into an ETF with every intention of holding those assets long-term—are not under attack. But the boutique industry that sprang up to build custom, single-investor ETFs as offshore-style tax shields has run straight into a brick wall.
The writing has been on the wall for months. The government realized that billions in capital gains were vanishing into custom-built ETF wrappers, and it just slammed the escape hatch shut.
