Bitcoin ETF Custody Risk: Coinbase Holds 80% of Assets

Coinbase now serves as the primary custodian for over 80% of U.S. Bitcoin and Ethereum ETF assets, creating a single point of concentration that puts roughly $74.7 billion in BlackRock’s iShares Bitcoin Trust ETF alone under one custodial roof.

The exchange disclosed in its Q3 2025 shareholder letter that it was the primary custodian for over 80% of U.S. BTC and ETH ETF assets as of quarter-end. Total assets under custody reached an all-time high of $300 billion, driven by ETF and corporate inflows.

Coinbase won eight of the 11 spot Bitcoin ETF custody mandates when the products launched in January 2024. Each of those eight issuers independently selected Coinbase as their primary custodian, according to a company blog post detailing its custody security practices.

BlackRock’s IBIT illustrates the scale of the dependency

BlackRock’s iShares Bitcoin Trust ETF reported net assets of $74,705,557,367 as of June 30, 2025, with 696,875 bitcoin held at fair value. Coinbase Custody Trust Company is listed as the fund’s bitcoin custodian in its SEC Form 10-Q.

The same filing names Anchorage Digital Bank as an additional bitcoin custodian for IBIT, but notes it had not yet been operationalized. BlackRock stated it had no current plans to move any of the trust’s bitcoin to Anchorage.

That detail is significant. Even the largest spot Bitcoin ETF, despite having a named backup custodian on paper, keeps its entire bitcoin balance with Coinbase in practice. For investors watching how regulators have shifted their crypto enforcement posture, the custody structure raises questions about infrastructure resilience rather than regulatory compliance alone.

What custody concentration means for ETF investors

ETF custody is distinct from asset ownership. Investors in IBIT or other spot Bitcoin ETFs own shares in a trust, not the underlying bitcoin. The custodian holds and secures the actual coins. When one custodian handles the vast majority of those coins across multiple products, any operational disruption at that custodian could ripple across the ETF market simultaneously.

This is not a claim that losses have occurred. It is a structural observation: eight of 11 ETF providers chose the same custodian, and that custodian now holds over 80% of combined BTC and ETH ETF assets. A compliance issue, outage, or security incident at Coinbase would not affect just one fund but potentially most of the U.S. spot Bitcoin ETF market at once.

The concentration also creates counterparty risk that differs from traditional ETF structures. In equity ETFs, custody is spread across multiple prime brokers and depositories. In spot Bitcoin ETFs, the custodial layer is far more consolidated, a reality that investors weighing whether to hold through volatility should factor into their risk assessment.

Why the $74.7 billion figure matters beyond one fund

IBIT’s net assets alone represent a substantial share of the total spot Bitcoin ETF market. When combined with the other seven funds that also use Coinbase custody, the total exposure through a single custodian is considerably larger than the $74.7 billion figure suggests.

Bitcoin traded at $71,111 at press time, down roughly 2.9% over the prior 24 hours. The Fear and Greed Index sat at 16, deep in “Extreme Fear” territory. In that environment, custody infrastructure matters more than usual, as stressed markets tend to expose operational weaknesses that calm markets conceal.

The broader concern is institutional access. Spot Bitcoin ETFs were designed to give traditional investors regulated exposure to bitcoin without holding the asset directly. If the custodial layer underneath those products is concentrated in a single provider, the resilience of that access point becomes a market-structure question, not just a company-specific one.

It is worth noting that the original headline’s claim of “over 80% of Bitcoin ETF assets” slightly overstates the verified language. Coinbase’s own disclosure refers to over 80% of U.S. BTC and ETH ETF assets combined, not Bitcoin ETF assets alone. The distinction matters for precision, though it does not diminish the concentration concern.

As broader crypto markets remain under pressure, the custody bottleneck adds another layer to the risk picture for institutional bitcoin holders. The infrastructure that underpins $300 billion in custodied assets rests heavily on a single exchange’s operational capacity.

Disclaimer: This article is for informational purposes only and does not constitute financial or investment advice. Cryptocurrency and digital asset markets carry significant risk. Always do your own research before making decisions.

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