Fidelity’s Timmer Says AI Bubble Risk Is Not Stock Valuations, but Debt

Fidelity director of global macro Jurrien Timmer said on Oct. 21, 2026 that stress in AI-related credit may be a more important bubble signal than stock valuations, pointing to CoreWeave’s bonds. The AI cloud provider’s bonds due in 2031 yielded 15.78% last Thursday, and five-year default insurance briefly cost more than 11% a year; S&P rates CoreWeave B+, below investment grade. CoreWeave, originally a crypto miner, reported debt rising from $21 billion at the end of 2025 to $35 billion by June 30, while $640 million in net interest expense took about a quarter of second-quarter revenue. CEO Mike Intrator said a contract backlog near $104 billion on June 30 more than covers debt obligations.