Basically any time i pull up the same perp contract on two different exchanges the funding rates are different in ways that don't obviously explain themselves, and it's been bugging me enough that i started tracking it systematically.

last week's example: ETHUSDT funding on bitmex was averaging +0.012% per 8h for three days while on bybit over the same window it was +0.034%. same underlying, similar OI profiles, nearly identical mark prices.

that's a pretty wide persistent gap, enough that a delta-neutral carry trade between the two would have printed real money if you could execute it without too much friction.

The obvious explanations i keep hearing are things like regional taker flow pushing inventory imbalances different directions on different exchanges or differences in how each one actually calculates the funding formula (the clamp ranges vary, premium component weighting varies), or taker flow skew that doesn't show up in public OI data. i buy all of those as partial explanations.…