BlackRock's iShares Bitcoin Trust (IBIT) acquired $195.6 million worth of Bitcoin in a single session, according to on-chain data from Arkham. The purchase lifts the fund's cumulative buying over the past 30 days to $1.57 billion.

Flow data puts IBIT's net inflow for the session at $195.57 million. No other US spot Bitcoin ETF contributed more that day. The category as a whole finished with a net inflow of just $102.67 million — less than half of IBIT's haul on its own.

The arithmetic leaves little room for interpretation. If one fund took in more than the entire category's net total, the remaining funds were collectively net sellers that session. IBIT effectively carried the group.

The positive print also reversed the prior session's direction. US spot Bitcoin ETFs had posted a net outflow of approximately $149 million before IBIT's buying turned the tally positive again. Bitcoin traded above $86,000 during the reported session.

A month of dominance

Zoom out to 30 days and the pattern holds. The spot Bitcoin ETF category drew approximately $2.99 billion in net inflows over that stretch, and IBIT remained the top recipient throughout. Set IBIT's $1.57 billion against the category total, and BlackRock's fund accounts for more than half of the month's net money on those numbers.

That concentration has operational consequences for the market. When a single vehicle channels the majority of regulated Bitcoin demand, its creation and redemption activity carries outsized weight in the underlying market's order flow — and the divergence between IBIT and its peers widens with each session where the rest of the category nets negative.

How the flows become buying

IBIT operates through authorized participants: large trading firms that create new ETF shares when investor demand rises and redeem them when it falls. When investors buy more IBIT shares than are available, new shares get created. To keep each share backed on a 1:1 basis with Bitcoin, the fund must acquire the matching amount of the asset.

That mechanical link explains why IBIT flows attract close attention from traders. They translate brokerage-account demand directly into buying pressure on the underlying asset, with no discretionary step in between.

From January 2024 launch to benchmark status

IBIT launched in January 2024, after the US Securities and Exchange Commission approved spot Bitcoin ETFs. It is now the largest US spot Bitcoin ETF by assets under management, with AUM reaching $109.34 billion in the latest reporting.

The fund charges a 0.25% management fee, and BlackRock brings a distribution network that reaches advisers, wealth platforms and institutions — channels smaller issuers struggle to access. That distribution advantage is the structural driver behind the flow concentration: financial advisers allocating client capital into Bitcoin exposure route through the largest, most liquid vehicle available.

A growing share of institutional demand for Bitcoin now moves through regulated products like IBIT rather than direct coin ownership. A month of $1.57 billion in IBIT buying points to a sustained allocation trend rather than a one-day anomaly, and the category's swing from a $149 million outflow to a $102.67 million inflow in consecutive sessions shows how dependent aggregate demand has become on a single fund's creations.

At $109.34 billion in AUM, IBIT has become the benchmark the rest of the spot Bitcoin ETF market gets measured against — and if current flow patterns persist, the gap between BlackRock's fund and its competitors will keep widening through the coming quarters.