Institutional investors hold a record 44.2% of the Bitcoin in US spot ETFs, and BlackRock plus Fidelity are capturing more than 90% of net flows from new capital. IBIT alone runs 61.3% of ETF assets and about 52% of Bitcoin options volume, while more than 80% of the underlying Bitcoin sits with a single custodian. The result is a two-issuer oligopoly over marginal Bitcoin supply that no proposed US rule currently addresses.
Two asset managers now decide where most new Bitcoin ETF money goes. BlackRock and Fidelity took more than 90% of net flows from fresh capital, according to Crypto Economy, while institutional investors lifted their share of the Bitcoin held in US spot ETFs to a record 44.2% in 2026.
"The concentration is not a market accident," the report said, describing self-reinforcing advantages that marginalize smaller issuers. BlackRock's IBIT alone manages 61.3% of assets across all US spot Bitcoin ETFs, a share larger than the next three funds combined.
The flow record is not a straight line. Between May and June, the funds logged 13 consecutive days of net outflows totaling roughly $4.4 billion, and June closed with $4.5 billion in redemptions. August reversed the trend with $3.52 billion of inflows, the strongest month of the year, and September added $3.8 billion in three weeks. Through it all, the two largest issuers kept absorbing the bulk of whatever arrived.
13F filings show institutional positions rose 7.5% in the second quarter, from 498,389 to 535,723 BTC, while Bitcoin fell 14.2%. Retail investors cut holdings by more than 100,000 BTC over the same stretch. Institutions bought the decline; retail sold it.
The asset share understates the structural advantage. IBIT carries roughly 52% of Bitcoin options market volume, which lets authorized participants hedge inventory across listed contracts and narrow the risk of creation and redemption activity. Market makers gravitate to the deepest book, tighter spreads draw more volume, and more volume deepens the book. Smaller funds including ARK 21Shares and Bitwise have seen weekly flow share fall to single digits. Hashdex's DEFI ETF liquidation, the first such closure, landed in a week when IBIT absorbed 80% of positive net flows.
The buyer base has broadened even as the vehicle base narrowed. JPMorgan raised its IBIT stake 25.5%, to 10.4 million shares from 8.3 million, valued near $355.7 million. Morgan Stanley lifted its position 23%, to roughly 16.5 million shares. Goldman Sachs holds more than $700 million of IBIT, Harvard's endowment held 3.04 million shares worth about $101.4 million, and a UAE wealth fund held a position valued near $763.6 million. Pension funds and endowments now reach Bitcoin through ordinary brokerage accounts.
More than 80% of the Bitcoin underlying US ETFs sits with Coinbase. An operational failure, a successful cyberattack, or a liquidity squeeze there would hit nine of the 11 approved ETFs at once. An investor holding IBIT, FBTC, and GBTC does not diversify counterparty risk; the investor holds the same Coinbase exposure through three tickers.
That is the tension in the 44.2% figure. ETF shares carry price exposure but no governance rights over the Bitcoin network — holders cannot vote on protocol upgrades, run nodes, or choose miners. A regulated custodian can freeze addresses under court order, and an issuer can suspend creations or redemptions in extreme conditions. The disintermediation Bitcoin was built around becomes reintermediation at the access layer.
Regulators have not addressed the structure. The SEC opened a 60-day comment period on novel ETFs in June 2026 with specific questions on crypto assets, and NYSE Arca proposed a rule requiring at least 85% of trust assets to meet eligibility standards. The CLARITY Act, under Senate discussion, would permanently exempt Bitcoin and Ethereum from securities laws if their ETFs were approved before January 2026. None of the three touches custody or issuance concentration limits.
The forward risk is mechanical. When two issuers control the majority of ETF assets, a single large allocation decision or a custodian restriction can move spot price, because selling pressure or a halt in share creation transmits directly into the underlying market. Derivatives depth absorbs part of that shock without removing the dependence on a handful of actors. The next test is the flow data itself: if IBIT and FBTC keep taking more than 90% of net new capital through the fourth quarter, the marginal buyer of Bitcoin is effectively two asset managers and their custodian.
This article is for informational purposes only and does not constitute investment advice.
