What is open interest

Open interest is the stock of futures contracts that traders have opened and not yet closed. Each contract has a long and a short. Counting both sides once, in dollars, is the open interest. When a new long and a new short meet, open interest rises. When a holder closes, it falls. Volume is different. Volume counts how much traded. A market can trade a lot and end the day with the same open interest it started with, if every new position was matched by a close.

Hyperliquid is the current desk example. On October 10, 2026, a CoinGecko count put the venue at $15.6 billion of perpetual open interest, about 66 percent of the perp DEXes on that board. A second board the same day put the core markets at $11.94 billion and the HIP-3 venue trade.xyz at $3.56 billion. The two counts are the wide book and the split book. The story is here: https://cryptokeymedia.com/news/hyperliquid-open-interest

The number does not say whether the market is long or short. Every long has a short. Open interest can rise because new bulls and new bears both showed up. A separate board, the account long/short ratio, is what says which way the accounts lean. Ethereum's 75.2 percent long reading in that same note is an account count. It is not the open interest. Putting the two in one sentence without naming which is which is how a snapshot gets misread.

A dollar of open interest is also only as good as the price used to convert the contracts. Trackers multiply contract size by a mark price. If one site halves the figure so it does not double-count the long and the short, and another site does not, the same exchange can look twice as large. The October 10 gap between $15.6 billion and $11.94 billion was mostly scope, core markets versus core plus HIP-3, not a mystery. The next gap a reader sees may be a counting rule instead. The label on the column is the check.

Rising open interest with a rising price means new money is opening positions in the direction of the move, longs more than the shorts who are being squeezed, or simply more of both. Rising open interest with a falling price means new shorts are comfortable adding. Falling open interest means positions are being closed. None of the four combinations is an instruction. They describe whether the move is being joined or abandoned.

Liquidation cuts open interest in a hurry. A forced close is still a close. A crash that wipes leveraged longs will show a drop in open interest and a burst of volume at the same time. That pair, high volume and falling open interest, is the footprint of a flush. High volume and rising open interest is the footprint of new bets. The price candle looks violent either way. The open interest is what says which event it was.

Open interest is not the market cap, and it is not the coin supply. Market cap prices the coins that exist. Open interest prices the contracts that exist. A bitcoin perpetual's open interest can be larger than a day's spot volume, or smaller. It cannot be added to the market cap to produce a bigger bitcoin. The contracts are bets. The coins are the asset.

What comes next is the next print from the same tracker. A figure from CoinGecko and a figure from a venue's own API will not always match, and they do not have to. Hyperliquid's October 10 number is $15.6 billion on the wide count and $11.94 billion on the core count. Until those boards print again, open interest means the contracts still open, on the board the reader actually has in front of them.