GBTC vs IBIT: who actually custodies the Bitcoin, and on what terms

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August 19, 2026

5 min read

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For BlackRock’s iShares Bitcoin Trust (IBIT), the custody arrangement is a matter of public record: a Form 8-K filed with the SEC and dated April 7, 2025 discloses that BlackRock Fund Advisors signed a Master Custody Service Agreement adding Anchorage Digital Bank N.A. as a second custodian, with Coinbase remaining the primary holder of the trust’s Bitcoin, according to CryptoSlate’s reporting on the filing. For Grayscale’s Bitcoin Trust (GBTC), no such filing appears in the evidence gathered for this page. The only claim that GBTC uses Coinbase Custody Trust Company comes from Spark Money, a third-party ETF comparison tool, which does not cite a filing to support it.

What a spot Bitcoin ETF custody agreement actually covers

A spot Bitcoin ETF does not hold futures or derivatives. It holds actual Bitcoin, and something has to physically secure the private keys that control that Bitcoin. That entity is the custodian, and the agreement between the fund’s sponsor and the custodian typically spells out how keys are stored, what insurance applies, and what happens in edge cases like a blockchain fork.

The April 2025 IBIT filing is a useful worked example of what such an agreement contains, per CryptoSlate. It requires Anchorage to use cold storage for all private keys, to maintain insurance coverage, and to comply with provisions addressing blockchain forks and indemnification responsibilities. Anchorage is a federally chartered digital asset bank regulated by the Office of the Comptroller of the Currency, a detail CryptoSlate frames as relevant to the trust’s compliance posture.

Crucially, per CryptoSlate’s reporting, this was not a custody handover. Coinbase remained fully responsible for IBIT’s current custodial functions at the time of the filing, and no Bitcoin had been moved to Anchorage. CryptoSlate describes Anchorage’s role as standby, built for operational redundancy rather than immediate use. The trust’s fee arrangement, structure and investment objectives were unchanged.

The common misreading

A filing that adds a second custodian is easy to misread as a filing that moves the Bitcoin. It does not. Per CryptoSlate’s account of the 8-K, Anchorage was brought on as a contractual backup, not an active holder, and BlackRock’s public description of the move ties it to risk mitigation and long-term operational redundancy rather than any dissatisfaction with Coinbase.

What is known, and not known, about GBTC’s custody

Spark Money’s comparison table states that Coinbase Custody Trust Company serves as custodian for 8 of the 11 original spot Bitcoin ETFs, a group that would include GBTC by elimination, since Spark Money separately identifies Fidelity’s FBTC as the only major fund that does not rely on Coinbase at all, using Fidelity Digital Assets instead. Spark Money also states that BRRR added BitGo Trust Company alongside Coinbase, and that ARKB and HODL have adopted multi-custodian models. None of these custody claims are attributed to a specific SEC filing, prospectus, or other primary document in the evidence gathered here. They should be read as claims from a comparison and marketing tool, not as confirmed fact on the level of the IBIT 8-K.

This matters because the two funds are not symmetrical in what a reader can verify. IBIT’s custody structure traces to a dated regulatory filing with specific contractual terms. GBTC’s traces to an aggregator’s summary table with no equivalent citation.

The broader concentration question

Spark Money frames Coinbase’s role across most of the original 11 funds as a concentration risk, and says several issuers have responded with multi-custodian arrangements: IBIT with Coinbase and Anchorage, BRRR with Coinbase and BitGo, and ARKB and HODL also described as multi-custodian. If accurate, a large share of the roughly $91 billion in combined US spot Bitcoin ETF assets that Spark Money reports as of March 2026 would rest, for primary custody, on a single company. But that figure and the underlying custodian count are single-sourced to Spark Money in this evidence set, with no SEC filing behind the ‘8 of 11’ claim.

Spark Money also describes all spot Bitcoin ETFs, including GBTC and IBIT, as structured as grantor trusts that hold physical Bitcoin and settle authorized-participant transactions in cash rather than in-kind, which it says introduces minor tracking error against spot price. This is presented as an industry-wide structural feature rather than something specific to either fund.

The size and fee gap, for context

The custody question sits alongside a fee and size gap that has been documented since the two funds’ first months of trading. Bitcoin Magazine reported that, as of May 28, 2024, IBIT held over $20 billion in assets and 288,670 Bitcoin, overtaking GBTC’s $19.7 billion in assets and 287,450 Bitcoin holdings; on the Tuesday it described, GBTC saw a $105 million outflow while IBIT gained over $100 million, and Fidelity’s Bitcoin ETF trailed both at $11 billion. Bloomberg’s coverage of the same event, which this page can cite only by headline, also described IBIT overtaking GBTC as the world’s largest Bitcoin ETF; CoinDesk’s markets column that day likewise flagged the flip as a market event, per its headline. Neither headline-only source is quoted here beyond that description, because the underlying article text was not available for verification.

By March 2026, per Spark Money, the gap had widened. IBIT’s expense ratio stood at 0.25% against roughly $70.6 billion in assets, while GBTC’s stood at 1.50% against roughly $14.9 billion. Spark Money also reports that the first year of all 11 original spot Bitcoin ETFs combined drew over $56 billion in net inflows, and that the Grayscale Bitcoin Mini Trust, a separate lower-fee fund launched July 31, 2024, was seeded with roughly 10% of GBTC’s Bitcoin holdings.

What this page does not tell you

This page cannot confirm GBTC’s custodian from a Grayscale SEC filing. The only claim in the evidence gathered comes from Spark Money, a comparison and marketing tool that names no underlying document, so that claim is reported here as unverified, not as fact.

The custody detail on IBIT is accurate only as of CryptoSlate’s reporting on the April 7, 2025 filing. Any custodian change since then, including whether Anchorage has moved from standby to active use, would not appear on this page.

Spark Money’s AUM and fee figures are tied to a March 2026 reference point inside the article, but the page itself carries no clear publication date and is a comparison tool rather than a newsroom. Its numbers are treated here as unaudited and are not attributed to any primary filing.

This page does not independently verify the custody terms Spark Money describes for other funds, including BRRR, ARKB, HODL and FBTC. Those claims are repeated here as single-sourced statements, not confirmed facts.

Finally, what insurance, indemnification or fork-handling terms, if any, govern GBTC’s custody arrangement is not addressed anywhere in the evidence gathered for this page. Whether Grayscale has any plan for a backup or multi-custodian structure comparable to IBIT’s is likewise unknown from this evidence.