The §351 ETF Conversion

The newest tool in this section is the one that just lost most of its value, and you need to know both halves of that story — what it is, and what Treasury did to it in September 2026 — because advisors will keep pitching it. A 351 conversion uses the same nonrecognition rule that lets a founder incorporate without paying tax: under IRC §351(a), transferring property to a corporation solely for its stock, where the transferors control the corporation afterward, is not a sale. An ETF is a corporation for tax purposes, electing RIC treatment under IRC §851, “Definition of regulated investment company”. So you, usually alongside a handful of other investors, contribute your appreciated portfolio to a brand-new ETF on launch day, receive its shares, and carry your old basis into a listed, liquid wrapper that will never pass you a capital gain distribution, because the in-kind redemption mechanism of IRC §852(b)(6) purges the gains (section “Exchange-Traded Funds (ETFs)”).

The catch that makes this harder than it sounds is IRC §351(e), the same investment-company rule that forces exchange funds to hold 20% in illiquid assets. A transfer to a RIC is taxable if it “results in diversification.” The regulations supply the escape: a contribution does not diversify you if what you contribute is already a diversified portfolio, defined by the IRC §368(a)(2)(F)(ii), “Definitions relating to corporate reorganizations” tests — no single issuer above 25% of the portfolio’s value, and the five largest issuers together no more than 50% (Treas. Reg. §1.351-1(c)(6)). Cash and receivables are left out of total assets entirely (IRC §368(a)(2)(F)(iv)), so they cannot dilute a concentrated name; government securities are the one exception the regulation carves — they count in the denominator but never as an issuer in the numerator, unless you bought them to pass the test. The rule is why the strategy was never for the founder with one stock; it was for the person whose portfolio was already spread across fifteen or twenty positions but still carried a decade of gain.

The economics kept it a seven- and eight-figure product. Launching an ETF costs $200,000 to $300,000 up front plus an ongoing expense ratio, so practitioners put the entry ticket at $25 million of appreciated securities and the comfortable one near $100 million. By the time Treasury acted, roughly $22 billion of ETFs had been seeded this way, deferring as much as $6.5 billion of gain.^$†$

What died: diversification by conduit. The version that spread fastest went one step further. Your contributed portfolio met the 25/50 test but had nothing to do with the ETF’s stated strategy, so as part of the same plan an authorized participant bought creation units with the securities the ETF actually wanted (or cash to buy them), and shortly afterward redeemed those units in kind — taking your old stocks out the back door under §852(b)(6), which lets the fund distribute appreciated property without recognizing gain. Net result: you traded a portfolio you no longer wanted for a portfolio you did, and nobody recognized anything. In late September 2026 the IRS issued Rev. Rul. 2026-20 on exactly those facts and held that the ETF was “merely a conduit”: the step-transaction and substance-over-form doctrines collapse the plan, and you are treated as having made a taxable exchange under IRC §1001(a), “Determination of amount of and recognition of gain or loss” directly with the authorized participant, for every security of yours that went out in the redemption. The ruling amplifies Rev. Rul. 71-336, a 1971 holding on the same pattern with ordinary corporations, which is the IRS’s way of saying this is not new law but old law applied to a new wrapper.

The companion Notice 2026-62 tells you where the line sits. It “does not address, and expresses no view regarding” a §351 seed “with assets that are consistent with the ETF’s investment thesis and that are intended and expected to be retained by the ETF absent a substantial change in circumstances.” That sentence is the entire surviving strategy. It also flags three things to expect: further guidance that may apply retroactively, possible designation as a listed transaction (which adds disclosure on Form 8886 and penalty exposure), and a second target — the partnership variation, in which a non-diversified position goes into an exchange fund first, the fund assembles a portfolio that passes the 25/50 test, and the fund then does the §351 conversion. Treasury says plainly it is considering guidance that would deny IRC §721(a) nonrecognition to that chain or recharacterize it, while expressly leaving ordinary exchange funds alone.

The three tells, and the arithmetic. An examiner reading the ruling will look for a plan, a quick redemption, and a portfolio that came out materially different from what went in. Any one of them invites the argument; all three decide it. The exposure is not abstract. Take a California resident contributing $30 million of securities with $20 million of built-in gain. Sold outright, the bill is federal 20% plus 3.8% NIIT plus 13.3% state:

Under the conduit pattern, the ruling treats the gain in whichever securities the authorized participant carried out as recognized in the year of the launch. If those held 80% of the built-in gain, that is $16 million recognized and about $5.9 million of tax. The ruling is silent on basis, but the logic of the recharacterization is that you took a cost basis under IRC §1012(a), “Basis of property—cost” in what you are deemed to have received from the authorized participant and carried it into the ETF shares under IRC §358(a), “Basis to distributees”, so the same gain should not be taxed twice. Layer on the 20% accuracy-related penalty of IRC §6662, “Imposition of accuracy-related penalty on underpayments” for a substantial understatement, which becomes the 30% penalty of IRC §6662A, “Imposition of accuracy-related penalty on understatements with respect to reportable transactions” if Treasury lists the transaction and you failed to disclose it on Form 8886, and the “free” diversification cost more than selling.

What still works, and what to do instead.

Seed and hold

If your portfolio already passes the 25/50 test and you want a listed wrapper around that portfolio — an ETF whose mandate is, in substance, the stocks you own — §351 still delivers deferral, a basis carryover, and gain-free rebalancing inside the fund over time. The ETF must genuinely intend to keep the positions. Normal turnover later, driven by markets rather than by a launch-week plan, is what the notice carves out. Document the investment thesis before the contribution, not after.

Diversify through time, not through a conduit

If the point was to get out of what you own, the honest tools are the ones already in this section: a seven-year exchange fund (section “Concentrated Stock Positions”), which the notice explicitly does not touch; a collar or prepaid variable forward (section “Protective Collar”) to carry the position while you sell on schedule; a charitable remainder trust for the slice you would give away anyway; and a direct-indexing account that harvests losses to offset the sales you make (section “Tax-loss harvesting”).

Do not chain an exchange fund into an ETF

The partnership variation is the next ruling waiting to be written, and Treasury has told you it may apply it retroactively.

Re-underwrite any 2024–2026 conversion you already did

The ruling applies existing doctrine, so it reaches closed transactions inside the statute of limitations (section “How Long They Can Come After You”). If the facts match the conduit pattern, discuss amended returns and the disclosure calculus with counsel now, before the comment period closes and the next notice arrives.