What is statistical arbitrage trading?
Stat arb looks to profit from price differences.
Stat arb is focused on profiting from price changes in futures contracts, whether that is a change in price of the future versus the spot price, or another futures contract, depends on the specific strategy.
At its most basic level, a stat arb trade could involve selling a high priced contract and buying a low priced contract, or vice versa, in expectation that those prices will converge (or widen) over time.