The ETF Share Class of a Mutual Fund

A normal mutual fund can offer several share classes of the same underlying portfolio — say, an "Investor" class and an "Admiral" class with different fee levels — all owning a pro-rata slice of one shared pool of assets. Vanguard's innovation, protected by a patent from 1996 to 2023, was to make an ETF simply another share class of an existing mutual fund, rather than a separate standalone fund. The ETF share class holds the exact same underlying stocks or bonds as the mutual fund's other share classes, just packaged in a form that trades intraday on an exchange like a normal ETF, while the mutual fund shares still only price and transact once a day at net asset value.

The key benefit is tax efficiency inherited from the ETF mechanism: when large investors redeem ETF shares, they typically do so "in kind" (receiving a basket of the fund's actual securities rather than cash), which lets the fund avoid selling appreciated holdings and realizing taxable capital gains. Because the ETF share class sits inside the same legal fund as the mutual fund shares, the entire fund — including the traditional mutual fund investors who never touch the ETF at all — benefits from that reduced turnover and lower realized capital gains, an effect sometimes called the "ETF heartbeat" trade.

Since the patent expired in 2023, other fund sponsors have begun filing to copy the exact structure, though implementation still requires SEC approval fund by fund, and questions remain about how liability and costs are allocated between share classes when one class's trading activity benefits another.