Short Sellers Record $6B in October Paper Profits as CoreWeave and Nebius Slide on AI Debt Fears

Investors betting against US neocloud and data center operators have generated $6B in paper profits so far in October following a selloff driven by concerns over unsustainable, debt-fueled AI infrastructure expansion. According to data analytics firm ORTEX, short interest across CoreWeave, IREN, Nebius Group, Applied Digital, and Core Scientific ranged from about 20% to 26% of their free float, with about $17B of stock currently sold short across the five firms and share borrowing costs remaining cheap. Short sellers in Nebius Group — which previously secured a $3.5B credit facility — recorded $2.94B in paper profits so far in October as short interest rose from 15.4% at the start of 2026 to 20% of free float, though those positions remain at a $3.33B paper loss year-to-date. CoreWeave's stock slumped almost 30% this month, generating close to $1.7B in paper profits for short sellers as short interest climbed from 19.6% at the start of October to 23.7% of its free float. Short sellers also logged more than $1.2B in combined October paper profits across data center operators IREN and Applied Digital, alongside $115M in October paper gains on Core Scientific, where short interest reached 23.1% of its free float.