Investors’ daily waves of option sales are poised to slow a sustained stock rally back to record highs.Option-selling strategies have abounded in 2025, from exchange-traded fund overwrites to systematic zero-day to expiry trades and bank Quantitative Investment Strategies. On the other side, the dealers typically rebalance their positions each day by selling into rallies and buying dips.The slowing effect may be felt more on gains than drops, as JPMorgan Chase & Co strategists led by Bram Kaplan noted an increasing preference for selling calls over puts in recent weeks. Meanwhile, UBS Group AG points to a particular strategy — selling so-called iron condors — that is popular with retail traders.With investors focused on ever-shortening windows of volatility to manage risks, the influence of contracts expiring from zero to five days away has surged. Zero-day to expiry options in particular keep scaling new heights at about 60% of overall S&P 500 Index volume.The short iron condor strategy — where a trader sells a call spread above the current market level and a put spread below it — has become popular with some retail traders, boosting volumes. Positioning on one-day to expiry option trades in the S&P 500 — specifically via the short iron condors — may have helped contain recent rallies, according to derivatives strategists at UBS.“This 1DTE iron-condor flow is now leaving a very clear imprint on SPX options positioning profiles, to the extent that it may be influencing underlying price action,” said Kieran Diamond, derivatives strategist at UBS.The iron condor strategy is set up to collect premium as long as the market stays in a narrow range. Market makers holding the opposite side of such trades have more hedging to manage when the underlying price approaches the nearer call strike in the final 30 minutes of trading. The size of the spreads and the distance between the strike prices has increased in recent months, according to UBS.While overall market maker gamma positioning from 0DTEs is dynamic during trading hours, much of the flow is still from investors selling options. Dealer positioning is most extreme on the upside call strikes. The lower volatility on those increases the gamma per unit of notional, making the dealer hedging impact more pronounced.“The most significant risk sits to the upside, with SPX market makers managing very large long gamma exposure from the calls that the condor traders have sold to them,” said Diamond. “When managing this risk, market makers need to sell equities as the index moves up toward the strike, which makes it incrementally harder for the S&P to rally during the trading session.”The end of the day is particularly fraught. In the most extreme example from Oct. 24, S&P 500 dealer gamma reached a peak of around $90bn 10 minutes before the close, according to Diamond. This means that a roughly 0.1% move in spot would generate around $10bn in flow to be bought or sold.While that can be absorbed by the futures market, it isn’t without a price impact. In theory, markets may be more likely to gap-up outside of regular hours in Asia or Europe, as the dealer hedging needs subside at the close every day.“There were a number of sessions through October when the market seemed to struggle to break through the region where this long gamma is concentrated, but then rallied after the close once the majority of the options risk had expired,” said Diamond.That may offer opportunities to exploit such price distortions, for example buying a one-day option at the close every day and selling it back at the open the next morning. Dealer gamma resets daily from this flow, so positioning tends to flatten around the end of trading at 4 pm New York time.Some are sceptical about the market impact of a particular option strategy like the iron condor.“Of the 25 or so different things that are pushing markets in different directions, this is one of the 25,” said Chris Murphy, co-head of derivatives strategy at Susquehanna International Group.Murphy said it was simply “one of many factors” influencing the market. “It gets more attention than it deserves.”Also, there are questions about the sustainability of such systematic short option flows, especially if they are retail driven.“Any systematic short-option strategy generally harvests premium pretty well until a high volatility environment realises and then it kills the trade via convex losses,” said Garrett DeSimone, head quant at OptionMetrics. “Even if you have great risk management and you can time the exit points, you will likely end up being sidelined for such a long period that your investors will likely lose patience and redeem.”