US spot Bitcoin ETFs posted withdrawals worth $635 million in a single session. This marked the biggest single-day withdrawal from these funds since June, enough to take the October totals into negative territory. To those looking at fund flows as a metric of institutional demand, the number puts a damper on a week that looked like a rebound.Bitcoin ETFs suffer biggest daily outflow since JuneAccording to SoSoValue data, more than $635 million was withdrawn from US Bitcoin ETFs on October 22. The funds’ losses reversed the $528 million inflow registered by these funds during the previous session, pushing October totals into the red zone,It was also the worst single-day performance by the funds since June 25, when they recorded an outflow of $696 million. This comes after the funds recorded inflows of $1.08 billion in three consecutive sessions before Thursday. It was a period that came right after two weeks of outflows. However, BTC ETFs ended the week with a positive total of $443 million.IBIT gave back more than it took iniShares Bitcoin Trust (IBIT) by BlackRock turns out to be the main cause of the huge outflows. The largest player among all other funds lost around $254 million in one day.The fact is significant since IBIT gained as much as $235 million the previous day, along with Fidelity’s Wise Origin Bitcoin Fund (FBTC), which gained $212.7 million. In other words, the fund not only lost a whole day’s gain but also gave away $19 million on top of that. Without IBIT, the rest of the issuers would have lost around $381 million in total.Altcoin funds followed Bitcoin lowerThe sell-off was not confined to Bitcoin. The Ether ETFs saw about $110 million flow out in that day. Solana-related funds fell by about $9 million, while the Hyperliquid (HYPE) funds dropped by about $8 million. However, the XRP ETFs bucked the trend with about $3.6 million inflow.As for Bitcoin, it was largely range-bound on that day, trading in the 80,996-82,551 range following an intra-day high of $84,777 reached the previous day. Bitcoin price dropped by 5% over the last 30 days. BTC price hovered around $81,650 at the press time.$635M day against a $100B asset baseThe context helps prevent this figure from appearing like a rout. Since the launch of US spot Bitcoin ETFs in January 2024, their cumulative net inflows have reached $57.32 billion, while their total net assets are at $104.71 billion, according to SoSoValue figures. This equates to 1% of the total in a single day.Bitcoin had successfully maintained an $82,000 to $85,000 band throughout the timeframe in question despite the flows and those figures did not show any direct pressure on prices. If $635 million in redemptions could not get Bitcoin out of its trading band, then buyers elsewhere must be soaking up the selling. The big question now is whether the events on October 22 were just a one-off occurrence or marked a reversal, and whether inflows will continue to increase above the $57 billion mark.If you're reading this, you’re already ahead. Stay there with our newsletter.