How a spot Bitcoin ETF actually holds bitcoin, and what the fee pays for

If you buy a share of IBIT or FBTC, you own a claim on bitcoin sitting in a vault, not a promise backed by futures contracts or a bank's balance sheet entry. That distinction is the whole reason "spot" is in the name, and it's worth understanding what actually happens when you click buy.

Creation units and the custodian

A spot Bitcoin ETF doesn't buy BTC one share at a time. Authorized participants, big trading firms like Jane Street or JPMorgan, assemble large blocks of cash (or in a few cases, bitcoin itself) and hand them to the fund in exchange for "creation units," typically 25,000 to 50,000 shares at once. The fund's sponsor takes that cash, buys bitcoin on the open market, and sends it to a custodian. For BlackRock's IBIT, that custodian is Coinbase Custody. Fidelity's FBTC uses its own in-house custody arm.

The bitcoin sits in cold storage under the custodian's keys, and the fund's shares represent a fractional claim on that pool. When you sell your shares on the stock exchange, you're not touching bitcoin at all. You're trading a claim with another investor. Only APs interact with the actual creation and redemption of coins, which is why share prices track BTC's spot price closely but not perfectly.

What the expense ratio pays for

IBIT charges 0.25% a year. FBTC charges 0.25% too, after promotional waivers ended. Grayscale's GBTC still charges 1.5%. That fee isn't arbitrary. It pays for custody (storage, insurance, key management), fund administration, the marketing and legal overhead of running a registered '33 Act product, and the sponsor's profit margin.

Custody is the biggest line item conceptually, even if it's a small dollar figure at scale. Coinbase Custody insures its cold storage and runs multi-sig cold wallets audited by third parties. You're paying a management fee, in part, to never have to think about a seed phrase.

The SEC's approval order from January 2024 lays out the surveillance-sharing agreements and custody arrangements that got these funds approved after a decade of rejected applications. Worth skimming if you want the regulatory backstory on why this took until 2024.

The catch and what to check

The fee compounds. At 0.25% a year, a $10,000 position loses about $25 annually to fees, growing with the position's value, forever, as long as you hold. That's cheaper than most active funds but not free, and it's a cost self-custody doesn't have once you've paid the one-time cost of a hardware wallet.

Before buying, check three things: the actual expense ratio (not the promotional teaser rate), who the custodian is and whether they've disclosed audit practices, and whether the fund allows in-kind redemption or cash-only, which affects tax treatment and tracking error. None of this makes the ETF wrong for you. It just means you're paying someone else to hold the keys, and that has a price tag.