Bitcoin spot ETFs experienced a sharp reversal in the first two days of September, shedding $236 million on Monday before rebounding with $217 million in inflows on Tuesday, erasing roughly half the damage in a single session. The whiplash underscored how dependent the market has become on a single buyer: BlackRock’s iShares Bitcoin Trust, the world’s largest Bitcoin fund by assets.
IBIT accounted for $201 million of Monday’s outflow and then $206 million of Tuesday’s inflow, according to SoSoValue data. Fidelity’s FBTC posted $44 million in outflows on Monday but managed only $7 million on the rebound. Bitwise’s BITB was the only fund on the other side on Monday, taking in $8 million, while the remaining eight spot Bitcoin funds tracked by SoSoValue showed zero activity on both days. That means BlackRock effectively dictated the entire direction of the U.S. Bitcoin ETF market for two consecutive sessions.
The swings followed a dominant August for Bitcoin ETFs. A nine-session inflow streak through August 28 absorbed roughly $3 billion, including a weekly total of $1.92 billion that represented the strongest single-week inflow since the products launched in January 2024. August closed at $3.52 billion in net inflows, the second-strongest month on record behind March 2024’s $4.6 billion. But the September 1 outflow snapped that momentum, raising questions about whether the buying was driven by genuine conviction or short-term positioning that is now unwinding.
Ether ETFs painted a different picture. Grayscale’s Mini Trust and BlackRock’s iShares Trust extended their winning streak to 11 consecutive sessions, pulling in $87.68 million on Monday alone. XRP and Solana products also attracted fresh capital, suggesting that while Bitcoin flows whipsawed, allocators were rotating into alternative crypto exposures rather than exiting the asset class entirely. The divergence between Bitcoin and altcoin ETFs is notable because it implies that the outflow was not a broad risk-off move but something specific to Bitcoin positioning.
Bitcoin traded at $77,403 on Tuesday, down 1.6% for the week but still up 23% from its August 1 opening price. The price has hovered between $76,400 and $79,200 for five consecutive sessions, a tight range that suggests consolidation rather than a directional breakout. Solana and Zcash led the 24-hour decliners at roughly 3% each, while XRP, Tron, and Dogecoin dropped about 2%. Ethereum held near $2,380, down roughly 2% on the day but still up 31% from its August 1 level.
The macro backdrop has shifted decisively against risk assets. The CME FedWatch Tool now prices a 64% probability of a 25 basis point rate hike at the September 16 meeting, up from 34% just one month ago. Fed Chair Kevin Warsh’s Jackson Hole speech in late August signaled that sticky inflation remains the central bank’s primary concern, with energy prices elevated by the ongoing U.S.-Iran conflict pushing Brent crude above $95 per barrel. New York Fed President John Williams sounded somewhat dovish in a Tuesday address, but stopped short of pushing back on rate hike expectations, saying only that the committee needs to see more data before the September meeting.
September has historically been Bitcoin’s weakest month, averaging a negative 3.3% return through 2025. In each of the two prior years when August closed green, September posted declines of 7.3% and 8.0% respectively. The combination of hawkish Fed messaging, rising oil prices, and seasonal weakness creates a headwind that the ETF market may struggle to offset with inflows alone. Traders who bought the August rally may be taking profits ahead of a potentially difficult month, which would explain the outflow-rebound pattern rather than a clean directional move in either direction.
The concentration of flows in IBIT carries structural implications for the broader market. BlackRock’s fund has accumulated $99.6 billion in assets under management, putting the $100 billion mark within reach. That dominance means the broader ETF ecosystem depends on a single fund’s trading behavior. When IBIT moves, the entire market follows. When it pauses, the rest of the market goes quiet. This level of concentration is unusual for a product category that was designed to broaden institutional access to Bitcoin. It also raises questions about what happens if BlackRock’s flows slow or reverse for an extended period, particularly as competing products from Fidelity and Bitwise struggle to gain comparable traction in a market that increasingly looks like a one-fund show.
September 11 brings the August Consumer Price Index report, which will be the last major data point before the Fed decision five days later. If inflation runs hot, rate hike odds could climb further toward 70% or beyond, putting additional pressure on Bitcoin and risk assets. The September 15 Senate procedural vote on the CLARITY Act could offer some counterweight, but the bill faces opposition from lawmakers who want stricter stablecoin yield restrictions, and passage is far from certain. Meanwhile, the Solana spot ETF recently crossed $1 billion in assets, and Bitwise’s product continues to attract institutional inflows even as Bitcoin-focused funds see turbulence.
Bitcoin ETF assets across all U.S. spot products now total approximately $99.6 billion. The next two weeks will determine whether August’s strength was a genuine shift in institutional positioning or a temporary burst of momentum that is already fading. If inflows resume and the September CPI comes in mild, Bitcoin could test $80,000 again. If they do not, the seasonal pattern suggests a pullback toward the low $70,000s is the more likely path.
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