Bitcoin spot ETFs recorded a total net inflow of $618 million on September 21, according to SoSoValue data. The single-day surge highlights continued institutional capital allocation into regulated Bitcoin investment vehicles. Total net assets for Bitcoin spot ETFs now stand at $105.589 billion, with the ETF-to-market cap ratio reaching 6.31%. Cumulative net inflows have reached $55.8 billion since inception, underscoring sustained demand in the spot ETF market.