Falling rental prices alone would not overturn my thesis. Efficiency improvements, technological substitution and additional supply can lower prices even as adoption expands. I would become more cautious if sustained declines across comparable rental markets coincided with weaker utilization, contract cancellations and deteriorating customer economics. Prices alone cannot establish utilization or customer profitability.
4. Leverage
Leverage can turn a valuation correction into a financing crisis. The Federal Reserve’s May report described resilient banks alongside record-high hedge-fund leverage [21]. The IMF’s October analysis adds a more direct AI warning: 14 transactions since 2023 involved about $300 billion of equity and $650 billion of debt against $1.4 trillion of future revenue commitments [18]. Those commitments are not realized sales. Stress at a major customer could simultaneously impair revenue, investment values and debt. I therefore treat financing risk as yellow, with greater urgency than before.
Speculation also deserves a less reassuring label. Cboe reported that estimated retail options flow reached a record in September, even as overall Q3 options activity moderated [19]. Renaissance Capital’s public Q3 preview counted 30 US IPOs raising $32.8 billion, including SK Hynix’s $26.5 billion offering [20]. That concentration does not establish a broad flood of weak issuers, but neither does it rule out excess in private AI markets.
5. Vertical Price Action
Acceleration matters more to me than a large cumulative gain. What makes me cautious is not just that an asset rises a lot, but that the final leg becomes unusually steep or almost vertical. That pattern often reflects a shift from fundamentals-led repricing to momentum, leverage and fear of missing out.
Table 3 provides historical context for that warning sign. The episodes have different assets, contract structures and measurement windows; they are not comparable return benchmarks or a threshold that identifies a bubble. In particular, a semiconductor stock rally can reflect both earnings growth and speculation. I therefore view vertical price action as a warning signal that deserves attention, but not as conclusive evidence of a market-wide bubble.
Table 3. Historical Context for Rapid Price Acceleration
