How a spot bitcoin ETF actually holds bitcoin, and what the fee pays for
A look at the custody chain behind spot bitcoin ETFs and what the expense ratio actually covers.
If you buy shares of IBIT or FBTC in a brokerage account, no bitcoin ever touches your wallet. So where does the coin actually sit, and what are you paying for when the fund charges 0.25% a year?
The mechanics of creation
A spot bitcoin ETF issues shares through "authorized participants," usually large trading firms like Jane Street or Virtu. When demand for shares rises, an AP delivers cash (or in some structures, bitcoin) to the fund, and the fund's custodian buys or receives actual bitcoin to match. The fund then issues new shares to the AP, who sells them on the exchange. Redemption runs the same process backward: shares go in, bitcoin or cash comes out.
BlackRock's iShares Bitcoin Trust (IBIT) uses Coinbase Custody Trust Company as its sole custodian, holding the underlying bitcoin in cold storage under a custody agreement. Fidelity's FBTC self-custodies through its own Fidelity Digital Assets arm. You can check exact holdings and the custodian relationship in each fund's prospectus filed with the SEC; BlackRock's is public in its S-1 filing. As of mid-2024, IBIT held over 300,000 BTC, all routed through Coinbase's custody vaults, verified periodically by proof-of-reserves style attestations rather than continuous on-chain audits.
What the expense ratio buys
The fee, 0.25% for IBIT, 0.19% (after a temporary waiver) for FBTC, doesn't pay for trading bitcoin. It pays for three things: custody (keeping keys secure and insured), fund administration (share creation/redemption, NAV calculation, SEC reporting), and sponsor profit. Custody insurance is the detail worth checking. Coinbase Custody carries commercial crime insurance, but the coverage caps are often a fraction of total assets held, meaning a catastrophic breach wouldn't necessarily make every shareholder whole.
The tradeoff: convenience versus control
Holding IBIT means you never manage a seed phrase, never worry about sending BTC to the wrong address, and get standard brokerage protections like SIPC (which covers the shares as securities, not the underlying bitcoin itself). What you give up is direct claim on the coins. If Coinbase Custody or the fund sponsor faced insolvency or a dispute, your recourse runs through fund structure and bankruptcy law, not a private key you control. That's a meaningfully different risk profile than self-custody, even if day-to-day it feels the same as owning any other ETF.
What to check before buying
Read the prospectus section on custody arrangements and insurance limits. Confirm whether the fund publishes bitcoin holdings and wallet addresses (some do, some just report AUM). Compare the expense ratio against how long you plan to hold, since a 25 basis point gap compounds over years. And decide honestly whether you're buying bitcoin exposure or buying convenience, because a spot ETF gives you the second thing dressed as the first.