ARKB: the one Bitcoin ETF that refused to put everything at one custodian

What ARKB is

ARKB is a grantor trust that holds bitcoin and issues listed shares against it. It launched on 11 January 2024, on the same morning as ten siblings, under the SEC order that finally opened the category. Buy a share and you own a proportional claim on coins sitting in cold storage. The sponsor fee is skimmed continuously in bitcoin rather than billed in cash, so the amount of bitcoin backing each share drifts very slowly downward over time. That is the whole machine, and it is essentially the same machine in every fund on the US spot Bitcoin ETF list.

Because the design is standardised, the interesting questions on any individual fund are narrow ones: what does it cost, who holds the coins, and who stands behind the paperwork. ARKB has an unusual answer to the second question and a mixed answer to the first. It is the fifth-largest fund in the category with roughly $2.6bn against IBIT's $60bn, so nobody should pretend it is a contender for the top slot. It is, however, the only fund whose structure addresses a risk the rest of the category has quietly accepted.

Who actually runs it

Start with a correction, because it matters for how much weight you give other sources. The sponsor of ARKB is 21Shares US LLC. ARK Investment Management is the sub-adviser. A great many directories, comparison tables and news write-ups have this the other way round — ARK sponsors, 21Shares sub-advises — presumably because ARK's name comes first in the fund name and ARK's founder is the more recognisable public figure.

This is not pedantry. The sponsor is the entity with the contractual obligation to run the trust, appoint and remove custodians, set the fee and file with the SEC. Knowing that the answer is a Swiss-rooted crypto ETP specialist rather than a US active-equity manager tells you something real about why the fund is built the way it is: 21Shares has been running physically backed crypto products in Europe for years, and the multi-custodian habit came with it. Our page on the sponsors, custodians and authorised participants behind these funds sets out how the roles divide across the category.

Three custodians, and why that is the whole argument

Roughly 80% of every bitcoin held inside a US ETF sits with one company: Coinbase Custody. It is not that Coinbase is careless — it is that a single operational, legal or regulatory event at one firm would touch four fifths of the category at once. Fidelity's FBTC dodges this by custodying in-house through an affiliate. ARKB dodges it differently, and more thoroughly, by splitting the holdings across three separate providers: Anchorage Digital Bank, BitGo and Coinbase Custody.

Nobody else in the category does this. Several funds name an additional custodian in the filings and then say plainly that they have no current plans to use it — IBIT's relationship with Anchorage is exactly that. ARKB actually spreads the coins. If your objection to the category is operational concentration rather than the bitcoin itself, ARKB is the only product on the shelf that answers you.

One honest caveat. The precise legal entities named differ between 21Shares' own fund page and the language in the SEC filings, so the detail below the three names should be read as approximate rather than exact. The three-way arrangement itself is well documented; the entity-level breakdown is not something we would quote to two decimal places.

Custody

Fee, spread and the real cost of holding it

ARKB charges 0.21% a year with no waiver in force. That places it mid-table: below IBIT, FBTC, BRRR, BTCO and BTCW at 0.25%, level-ish with Bitwise's BITB at 0.20% and VanEck's HODL at 0.20%, above Franklin's EZBC at 0.19%, and well above the Grayscale Mini Trust at 0.15% and Morgan Stanley's MSBT at 0.14%. On $25,000 the fee is about $53 a year; on $100,000 it is $210. Against the cheapest fund in the category that is a gap of seven basis points, or $70 a year per $100,000.

The spread is the less comfortable number. ARKB's 30-day median bid-ask spread was 0.05% on 31 August 2026 — the widest of the five largest funds. IBIT quotes 0.03%, GBTC 0.02%, FBTC 0.03%, the Mini Trust 0.03%. Five basis points is not a disaster, but it is roughly double the best in class, and it is a cost you pay on the way in and again on the way out. Anyone who tells you spreads are a rounding error has not run the arithmetic for a trader who rebalances monthly.

Put the two together. A buy-and-hold investor making one purchase and sitting still pays the spread once and the fee every day, so the fee dominates and ARKB looks reasonable but unexceptional. An active holder crossing the spread every few weeks pays four extra basis points a year against IBIT in trading costs and saves four in fees, which is a wash — except that IBIT also gives you a vastly deeper options market. The full cost breakdown walks through how spread, fee and tracking difference combine.

The benchmark change nobody announced loudly

Effective 27 August 2026, ARKB's reference benchmark switched to the FTSE Bitcoin Index. Prior data was not restated. If you are pulling performance history for the fund and comparing it against another fund's tracking record, you are comparing two different measurement regimes stitched together at that date.

For a spot fund holding actual coins the practical effect is small — the benchmark determines the reference rate used for pricing and reporting, not what the fund owns. But it does mean a tracking-difference series that spans the change is not a clean like-for-like, and anybody building a fee-plus-tracking comparison across the category should note the discontinuity rather than smooth over it. Different funds reference different rates; MSBT tracks a CoinDesk settlement rate, for instance. This is one of several reasons we treat tracking difference as indicative rather than precise on the page explaining how these funds actually work.

Authorised participants and creation mechanics

The authorised participants named in ARKB's filings include Jane Street, Macquarie (USA), Virtu Americas, Marex and ABN AMRO Clearing USA. The filing says "among others", so treat that as an incomplete list rather than a roster. A new in-kind AP agreement with Macquarie carries the date 16 December 2025.

In-kind creation and redemption was approved by the SEC on 29 July 2025 and ARKB is covered by that order under the Cboe BZX rule. Whether it is operationally live at scale for ARKB is not something we can confirm. It is verified and running at scale for IBIT, whose annual report puts hard numbers on both sides of the in-kind ledger. For ARKB and FBTC the status is unconfirmed, and we would rather say so than imply otherwise. In-kind matters because it removes a cash conversion leg from the arbitrage loop, which is one of the things that keeps a fund's price glued to its net asset value — and, in turn, one of the inputs into a spread like ARKB's.

On the listed-options side, a live Cboe chain for ARKB was confirmed on 1 September 2026, alongside IBIT, FBTC, GBTC and the Mini Trust. Depth is nowhere near IBIT's, which is the world's largest bitcoin options market by open interest, so anyone building a serious options structure will end up at IBIT regardless of which fund holds their core position.

Who ARKB is for

ARKB makes sense if custody concentration is a live concern for you and you would rather not add a third of the category's operational risk to a portfolio you already think is risky. It makes sense if you want a mid-priced fund from a sponsor whose entire business is physically backed crypto products. And it makes sense as a diversifier alongside a larger position in a cheaper fund, which is a reasonable way to hold this exposure if you are nervous about any single trust.

It does not make sense if you are optimising on cost alone — the Grayscale Mini Trust is six basis points cheaper with a tighter quote. It does not make sense if you trade often or use options, where IBIT is untouchable. And it does not make sense if what you actually want is bitcoin you can move, in which case no ETF is the right instrument at all.

If you are still narrowing the field, three pages do the rest of the work. Our opinionated picks across the crypto ETF market sorts funds by what the investor is actually trying to do; the full directory by asset class covers ether, Solana, XRP, index and income products alongside the bitcoin funds; and the step-by-step buying guide covers order types and account choice once you have picked a ticker. If ether is also on your list, start with the spot ether fund comparison, where the staking question changes the arithmetic entirely.