What a call wall is
A call wall is the strike above the current price where call open interest, weighted by gamma, is largest. It is a single number produced by a gamma exposure model, and it is read as the upper edge of the range the options market is currently positioned around. Most services describe it as resistance, on the reasoning that the hedging desk assumed to be long the calls at that strike sells the underlying into a rally to stay delta neutral. It is not an observed order, a broker level, or anything anyone has committed to defend. SquawkFlow publishes the current SPX call wall free on the SPX gamma exposure page.
Gamma weighted, not raw open interest
The wall is not simply the strike with the most contracts on it. Open interest is weighted by gamma first, which is why a nearby strike carrying moderate size routinely outranks a distant strike carrying more. Two services ranking two different quantities will publish two different walls for the same underlying on the same day, so when figures disagree the first thing to check is which quantity each one ranked, not which one is broken.
This also separates the call wall from the absolute gamma strike, which drops the sign and takes the largest total gamma anywhere on the chain, above or below spot. The two answer different questions and land on different strikes more often than not.
The positioning it assumes
Whether the call wall behaves as resistance depends entirely on which side of those calls the dealer is on, and no exchange publishes dealer inventory. The convention every public gamma metric uses is the one stated in the SqueezeMetrics gamma exposure white paper: "Call options are sold by investors; bought by market-makers." Long calls are positive gamma, so the modelled dealer sells into strength, which is the deceleration people mean by a wall.
Run it the other way and the conclusion inverts. A dealer short those calls buys as price rises, which adds to the move instead of capping it. That is the same machinery as a gamma squeeze, and it is why a call wall drawn on a day when the convention is wrong does not merely fail, it points the wrong way. The convention is a reasonable prior rather than a measurement: Amaya, Garcia-Ares, Pearson and Vasquez reconstructed the actual aggregate market maker position in SPX and SPXW from proprietary Cboe records and reported in 0DTE Index Options and Market Volatility that "the gamma of the aggregate OMM position, while typically positive, is often negative."
Call wall and put wall
The put wall is the same construction below spot, on put gamma rather than call gamma, and the two are usually presented as a matched pair bounding a range. The delta arithmetic behind them does not mirror, which is the part most explanations get wrong: the standard story has dealers short the puts, and a dealer short puts sells into a decline rather than buying it. Call wall and put wall compared works both derivations through and sets out the four mechanisms that do explain why the lower level behaves as it does.
What SquawkFlow publishes
The SPX call wall on our free gamma page comes from a full-chain snapshot built each morning before the open, using Cboe settlement open interest crossed with implied volatility, re-pricing 19,544 SPX contracts on 2026-09-22. That count moves with the listed chain rather than being fixed. Because the input is settled open interest, the wall is fixed for the session. Intraday refreshes repoint spot, the implied range and the 0DTE magnet, not the wall. Any page showing a call wall ticking through the day is showing something other than settled open interest.
We publish no hold rate for the call wall. The one shown until August 2026 was withdrawn because it counted untested days as holds, and we have not replaced it with a figure we would stand behind.
Educational content, not financial advice. See our risk disclosure.