Bitcoin has fallen to around $81,800, down 2.7% since midnight UTC, as mixed earnings reports from Tesla and Meta have revived doubts over AI spending. This decline follows a late-Wednesday surge to nearly $84,800. The CoinDesk DeFi index also saw a significant drop of 5.6%, while the CoinDesk 80 lost 3.5%. Overall, altcoins experienced sharper declines than Bitcoin, with Ether losing 2.6% to near $2,400.