U.S. spot Bitcoin ETFs witnessed significant outflows totaling $194.6 million on Thursday, marking the largest withdrawals in two weeks. BlackRock's IBIT led the outflows with nearly $113 million, while Fidelity's FBTC saw over $54 million withdrawn. Ethereum ETFs also experienced $41.6 million in outflows, reversing gains from the previous day. The sell-off is attributed to arbitrage desks unwinding basis trades as the spot-futures spread narrowed. Investors are closely watching upcoming U.S. inflation data and the Federal Reserve's December 10 rate decision as potential market movers. Meanwhile, on-chain data indicates exchange balances have dropped to 1.8 million BTC, the lowest level in seven years.