BlackRock just gave IBIT a second set of keys.
On April 7, 2025, BlackRock Fund Advisors, acting as administrative trustee of the iShares Bitcoin Trust ETF, signed a custodial services agreement with Anchorage Digital Bank N.A. The filing landed the next day as an 8-K under Item 1.01, a material definitive agreement. The move adds a federally chartered digital asset bank as an additional Bitcoin custodian while leaving the existing Coinbase arrangement fully intact.
A Second Custodian, Not a Replacement
The 8-K is explicit on this point. The Trust's existing custody arrangement with Coinbase Inc., Coinbase Custody Trust Company, and affiliated Coinbase entities remains in force and is unaffected by the Anchorage agreement. BlackRock, as sponsor, retains sole discretion over how much Bitcoin sits at each custodian at any given time. The Trust is not required to hold any particular amount at either provider.
That discretion matters. It means the allocation between Coinbase and Anchorage can shift without a new filing, and investors will not necessarily see the split in real time. The custody structure is now more flexible, but also less transparent at the position level.
What the Anchorage Agreement Requires
Anchorage must establish and maintain one or more segregated custody accounts, controlled and secured on its own books, capable of receiving, safekeeping, and maintaining the Trust's Bitcoin. All private keys associated with Bitcoin held under the agreement must be kept in cold storage. Anchorage is also required to maintain specified insurance policies and coverage.
The agreement includes a fork provision. If the Bitcoin protocol forks, Anchorage may temporarily suspend services and, at its sole discretion, determine whether to support either branch, with the contractual obligation to use commercially reasonable efforts to avoid ceasing support for both branches simultaneously. That language is standard for institutional custody agreements covering a live blockchain, but it is worth understanding as a potential operational gap during a contentious fork event.
The indemnification structure runs both ways in the expected direction: the Trust indemnifies Anchorage against losses arising from the Trust's own material breach, violation of applicable law, gross negligence, fraud, or willful misconduct.
Custody Diversification as Infrastructure Risk Management
For a product of IBIT's scale, single-custodian concentration has always been the obvious operational risk to name. Adding Anchorage, which holds a federal bank charter through the Office of the Comptroller of the Currency, addresses that concentration without requiring a full custody migration. Anchorage is one of a small number of entities with that regulatory status in the digital asset space, which distinguishes it from most crypto-native custody providers.
The move also fits a broader pattern in institutional Bitcoin infrastructure. As spot Bitcoin ETFs have grown, the custody layer has attracted more scrutiny from both regulators and institutional allocators who want to see redundancy built into the plumbing. A second federally chartered custodian is a credible answer to that scrutiny.
IBIT's BTC Exposure Score sits at 90, reflecting that Bitcoin price movement is the central driver of the product's returns. The custody filing does not change that exposure. What it changes is the operational architecture underneath it.
Filing Risk and Event Density
IBIT's Event Momentum sits at 100, driven by the density of recent filings. The Filing Risk Score at 38 sits in the watchlist range, reflecting the material agreement disclosure and the eight added and eight removed risk-factor candidates identified in the most recent annual filing comparison, without reaching the elevated threshold. The custody agreement itself is an operational enhancement rather than a distress signal, but the combination of active filing cadence and a material agreement disclosure keeps the disclosure pattern worth tracking.
The risk-factor diff between the February 2026 and March 2025 10-K filings flagged one materially changed Item 1A candidate alongside the additions and removals. Whether any of those changes address custody concentration risk directly would require a line-by-line review of the annual filing.
The Allocation Question Stays Open
The filing that would change this read is any future disclosure showing how BlackRock has actually allocated Bitcoin between Coinbase and Anchorage. The 8-K establishes the legal framework and the operational requirements. It does not tell investors how much Bitcoin has moved, or will move, to the new custodian. That allocation remains inside BlackRock's discretion and outside the current disclosure perimeter.
Research only. Not investment advice.