US-listed spot Bitcoin exchange-traded funds (ETFs) delivered their strongest month of 2026 in August after Bitcoin surged 25%. However, the momentum has already been tested by a sharp reversal in September.
Monthly Bitcoin ETF flows (Source: SoSoValue)
Spot Bitcoin ETFs attracted $3.52 billion in net inflows during August, up dramatically from just $172 million in July. The total was their strongest month since October of 2025. Bitcoin, meanwhile, gained roughly 25%, and recorded its strongest monthly performance since November of 2024.
Bitcoin ETF Assets Close In on $100 Billion
August's inflows erased roughly two-thirds of the funds' 2026 deficit. Year-to-date net outflows fell from approximately $5.29 billion at the end of July to just $1.77 billion.
Investors poured money into the products on 16 of August's 21 trading days, including a nine-session streak between Aug. 17 and Aug. 27.
Perhaps more striking was the increase in assets held by the funds. Total net assets jumped about 31% from $76.29 billion at the end of July to $99.61 billion by the end of August, which brought the $100 billion milestone within touching distance. Monthly trading volume also climbed by about 49% to $58.63 billion.
BTC’s price action over the past month (Source: CoinCodex)
The rise in ETF assets outpaced Bitcoin's roughly 25% price gain. This could mean that the increase was not simply the result of higher BTC prices. Fresh capital played a meaningful role in expanding the funds.
September Bitcoin ETF Outflow Raises a Red Flag
The strong August finish has not carried cleanly into September. US spot Bitcoin ETFs recorded $236.46 million in net outflows on Sept. 1. This reversed the previous session's $216.70 million inflow and was the largest daily withdrawal since July 31.
BlackRock's iShares Bitcoin Trust (IBIT) accounted for the vast majority of the selling after losing $201.18 million, or roughly 85% of the day's total outflows. Fidelity's FBTC lost another $43.67 million, while Bitwise's BITB attracted $8.38 million.
Interestingly, the weakness was not shared across every crypto ETF category. Spot Ethereum ETFs attracted around $11 million on Tuesday, while XRP ETFs recorded approximately $14.4 million in inflows.
