When Is a Cross-Venue Funding-Rate Spread Worth Trading? Public-Data Evidence on Forecastability and Cost Coverage

Cross-venue perpetual-futures funding spreads are often presented as arbitrage opportunities, yet a quoted differential is neither a forecast nor net trading income. We study when settled funding differences can cover four-fill execution costs. Public APIs supply 121,864 funding records for eight major contracts on Gate, Hyperliquid, and Pacifica, aligned into 521 eight-hour blocks from May to November 2026; current public books on those venues and Paradex provide a separate cost snapshot. The median absolute spread is 0.45 bp per eight hours and the 99th percentile is 2.99 bp. Out of sample, a capped forecast reduces MAE from 0.430 to 0.399 bp relative to last-value persistence, with significant Diebold–Mariano improvements. This statistical gain does not create economic feasibility: no candidate generates a 24-hour entry at a 34 bp hurdle, while sparse 72-hour entries at 20 bp lose money in the funding-cash proxy. Probability forecasts underperform a training-frequency baseline. The evidence supports a break-even discipline rather than a claim of persistent arbitrage.