SEBI is reviewing the Closing Auction Session (CAS) for equity stocks after it triggered significant volatility on derivatives expiry days. Launched in August 2026, the session caused sharp price swings in indices due to a timing mismatch. Regulators now plan to issue a consultation paper to address these risks.
The Securities and Exchange Board of India (SEBI) has initiated a review of the recently introduced Closing Auction Session (CAS) for equity stocks. This decision comes after the mechanism, which began on August 3, 2026, caused unexpected price swings during the market close. The regulator confirmed on September 3, 2026, that it is examining the current settlement price methodology and intends to release a consultation paper to propose potential changes.
The CAS was implemented as a 15-minute window from 3:15 PM to 3:30 PM, with the official closing price finalized by 3:35 PM. Its primary goal was to improve price discovery and transparency in the cash equity segment. However, the system has faced criticism for creating a dangerous timing mismatch with the derivatives market, which continues to trade until 3:40 PM.
On derivatives expiry days, this five-minute gap—where the cash market is closed but derivatives are still trading—has led to liquidity issues. The cash market, which needs to be stable to set closing prices, has struggled to absorb the massive volume of expiry-related trades. This has resulted in extreme volatility, with some market indices like the Sensex experiencing sudden, sharp swings of approximately 2,000 points during the auction session. Market participants have raised concerns that these 'price shocks' make the market feel more like a lottery than a fair trading environment.
A significant part of this problem is linked to the high concentration of short-term options, specifically those expiring the same day, often called 0DTE options. Because so many traders use these contracts, the market experiences high sensitivity to price movements near the close. When the underlying cash market lacks enough depth to support these massive adjustments, the result is heightened volatility that can negatively affect investors.
Regulators are now looking to fix the settlement price methodology to ensure that the auction process better aligns with the needs of both the cash and derivatives markets. For investors, this regulatory review is a key development. The upcoming consultation paper will likely outline new rules to reduce these sudden price swings and improve the stability of the closing session.
The next important update for market participants will be the release of the SEBI consultation paper. Investors should track how the regulator plans to modify the timing or the price calculation method, as these changes could fundamentally alter how indices settle on expiry days and reduce the risk of extreme price manipulation at the end of the trading session.