Perp open interest: and what it tells you

Open interest = capital with skin in the game

Open interest, often shortened to OI, is the total notional value of all open perpetual futures contracts across the market at a given moment. If the BTC perp market has $20 billion in open interest, that's $20 billion of position size currently open between all the longs and shorts. It's a snapshot of how much capital has skin in the game right now.

Volume and open interest are not the same thing. Volume counts every trade — including trades that close existing positions. Open interest only changes when a new contract is opened or an existing one is closed. Two traders opening a fresh long and short between them adds to OI. Two traders closing their positions against each other subtracts from OI. Two traders trading with each other where one was already long and one was already short — that's volume without any change in OI.

Here's how to read OI in context. Price up + OI up = new longs aggressively entering, fresh capital chasing the move. Price up + OI down = the rally is mostly short covering, not new buying. Price down + OI up = new shorts aggressively entering. Price down + OI down = longs exiting, capitulation. The same chart can tell two very different stories depending on which one is happening.

Big OI levels also matter because they show concentration. When OI climbs sharply into a price level, a lot of money is now exposed near that price. If price moves against that exposure, a lot of positions will need to close — sometimes orderly, sometimes not. OI doesn't predict direction; it tells you where the fuel is stacked.

Recap: OI is the size of the perp market's open book. Rising = new positioning. Falling = exits. Pair with price direction to see who's entering and who's leaving.