Open Interest: Change in OI, Expiries and OI by Strike Explained

Open interest is the number of option contracts that are still open: opened and not yet closed, exercised or expired. It measures positioning, not trading. Vyreon reports how open interest changed in expiries listed on both days, separately from expiries that simply passed, because the raw total change mostly tracks the expiry calendar.

Open Interest Vs Volume

Volume counts contracts traded during the session.
Open interest counts contracts still outstanding afterwards.

A contract traded back and forth all day can leave open interest unchanged. Volume alone cannot tell you whether positions were opened or closed; the change in open interest can.

Why Open Interest Is As Of The Previous Close

Open interest is finalized by the options clearing process overnight, so the figure published for a session reflects positions at the previous session's close. Vyreon labels every open-interest figure with that date.

Change In Open Interest

The raw change in total open interest misleads around expiries: when an expiry passes, all of its contracts leave the total, even if nobody closed a position. Some of the most active ETFs list an expiry every trading day and many securities list weekly ones, so the raw total often falls for calendar reasons alone. Vyreon splits the one-session change into three parts:

Contracts open on both days: the change in open interest across expiries listed on both records. This is the cleanest view of positions opened or closed.
Expired: open interest in expiries that passed between the two records.
Newly listed: open interest in expiries that did not exist on the previous record.

The parts add up exactly: total change = change in contracts open on both days − expired + newly listed.

Illustrative example: yesterday's record shows 1,000,000 open contracts, 150,000 of them in an expiry that has since passed. The other expiries grew from 850,000 to 880,000, and a new expiry opened with 10,000. Total open interest fell by 110,000, yet open interest in contracts open on both days rose by 30,000 (+3.5%).

Vyreon's five-session measure of how open interest shifted across expiries follows the same rule: it compares only expiries alive at both endpoints.

Open Interest By Strike

Rather than list every strike, Vyreon summarizes where open interest sits with open-interest-weighted centres:

Call centre, put centre and overall centre, shown as strike prices. Each is the open-interest-weighted average distance of strikes from the closing price, measured in log terms and converted back to a strike.
Call–put separation: how far apart the call and put centres are.
Spread (width): how widely open interest is dispersed around the overall centre.
Average days to expiry of the open contracts.

A put centre well below the price means open puts are weighted toward strikes far out of the money. Open interest alone does not show whether they are hedges.

How Vyreon Measures It

Open interest is the reported figure for each listed contract, as of the previous session's close, totalled for calls and puts along with how concentrated it is. The change decomposition uses the reported totals per expiry and checks that they add up to the reported total on both days. Centres weight each contract's strike by its open interest.

What Open Interest Does Not Tell You

Who holds the contracts or which side (buyer or seller) they are on.
Whether positions are hedges, parts of spreads, or directional bets.
Whether a rise is "new money", bullish or bearish. It counts contracts, not intent.
Where the price will go. Concentrations, max pain and gamma "walls" are not price targets.

Sources

The Options Clearing Corporation (OCC), Characteristics and Risks of Standardized Options, the options disclosure document: how listed options are opened, closed, exercised and cleared.
John C. Hull, Options, Futures, and Other Derivatives (Pearson, many editions): open interest and trading volume.