If you own a single stock that has quadrupled and you have been waiting for a legal way to diversify without writing a large check to the IRS, late-September news from Washington changes your calculus. The Treasury Department and the IRS issued new guidance on September 28, 2026, to shut down the most aggressive version of the Section 351 ETF conversion, the strategy that let wealthy investors seed a brand-new ETF with appreciated stock and walk away with a diversified fund without recognizing a taxable gain.
Bessent wrote on X that “our message on these conversions is clear: they don’t work under existing law,” and that Treasury is serious about cracking down on transactions designed to dodge taxes or exploit the federal tax code.
What the Strategy Was, and What the Ruling Killed
A Section 351 conversion works by letting an investor turn a portfolio of assets into an ETF, typically so they can rebalance winning holdings without paying an immediate tax bill. Technically it is a deferral, since tax will still be owed when any shares in the ETF are eventually sold.
The version Treasury targeted was more aggressive than the basic exchange. Revenue Ruling 2026-20 recharacterizes prearranged Section 351 transactions in which investors contribute appreciated securities to an ETF and quickly redeem, emerging with a materially different portfolio, as a taxable exchange under Section 1001 with the authorized participant rather than a tax-free Section 351 contribution. That is the maneuver Bessent called a conduit: seed the fund with concentrated stock, let it be distributed out through an in-kind redemption, and pocket a diversified basket with no tax event recorded.
A Bloomberg analysis of SEC filings identified about $22 billion of ETFs created through Section 351 exchanges, holding roughly $22.1 billion at launch and deferring at least $6.5 billion in embedded capital gains, with activity ramping notably since 2024. The government’s new position is that it can challenge the targeted, prearranged swap under existing law. Notice 2026-62 also flags a broader set of fund strategies for possible future guidance and exam scrutiny, and it notes that future action could include steps that apply prospectively.
What Survives the Crackdown
The ruling does not eliminate Section 351 ETF seeding entirely. As Notice 2026-62 puts it, the government is not addressing, and expresses no view on, using a Section 351 transaction to seed a newly established ETF with assets that are consistent with the ETF’s investment thesis and intended to be retained absent a substantial change in circumstances.
The standard Section 351 exchange, in which an investor contributes a pre-diversified basket into a fund whose prospectus matches those holdings, and then holds the resulting ETF shares rather than immediately redeeming, is not the fact pattern addressed by Revenue Ruling 2026-20. Section 351 generally lets investors transfer property to a corporation in exchange for its stock without recognizing a capital gain, but transfers involving an “investment company” have special diversification rules. In general terms, the relevant diversification test is that no single issuer can exceed 25% of the portfolio’s value, and no more than 50% of the value can be invested in the securities of five or fewer issuers.
What Concentrated-Stock Holders Should Consider Now
For investors who own one dominant position and cannot yet meet the diversification tests for a standard 351 exchange, other tools remain available. Direct indexing can help unwind a position over time while harvesting offsetting losses. An exchange fund contribution can provide tax deferral, but the practical path to receiving a diversified basket is commonly framed around a seven-year holding period, and many funds layer on their own contractual limits and liquidity terms.
The broader lesson for wealth builders is not that tax-efficient diversification is dead. It is that strategies built on distance from a law’s original intent carry a shelf life. The September 28, 2026 guidance is explicit about its concern with transactions that combine technical nonrecognition rules with prearranged steps to achieve a tax result Treasury views as disconnected from economic substance. That framing matters: the government is still gathering information on related tactics, meaning further guidance on in-kind redemption timing strategies and exchange-fund-plus-351 combinations may still be ahead.
The Wealth Builder Takeaway
Legitimate tax planning around a concentrated position is not speculation; it is sound portfolio management. But any strategy that depends on regulatory ambiguity rather than a clear statutory foundation deserves extra scrutiny before execution. The investors best positioned after the September 28, 2026 guidance are those who had already chosen durable, well-documented methods: gradual selling against tax-loss harvesting, properly structured standard 351 exchanges that are not built around a prearranged, rapid swap-out, or exchange funds with their long holding discipline intact. Diversification remains the goal. The tool you use to reach it now needs to survive a closer read from the IRS.
