SEBI’s proposed changes to the Closing Auction Session could significantly influence the way India’s equity and derivatives markets operate at the end of the trading day.
Thank you for reading this post, don't forget to subscribe!The regulator is reviewing both the auction mechanism and the methodology used to calculate settlement prices for derivatives contracts.
The review follows the implementation of CAS on August 3, 2026. The system was introduced to improve closing-price discovery by concentrating market liquidity into an auction rather than relying solely on continuous trading during the final 30 minutes.
The closing price is more important than it may appear.
It is used not only to show where a stock finished the day but also for derivatives settlement, index-related calculations and other financial-market purposes. That means any major change in the closing-price mechanism can have consequences across the market.
SEBI’s original decision to introduce CAS was based partly on the argument that auction-based systems can produce a more representative closing price. The regulator wanted the final price to reflect a broader pool of market interest.
However, the new system created difficulties when combined with derivatives trading.
Derivatives contracts continued to operate around the closing period, and the relationship between the CAS price and the price used for expiry settlement became a major concern.
The issue became particularly visible during expiry sessions, when futures and options positions can react sharply to changes in the underlying price.
Market participants raised concerns about volatility and the possibility of price dislocations. SEBI subsequently announced that it would review the settlement methodology after receiving feedback from stakeholders.
The latest proposals offer two potential solutions.
The first is a blended VWAP model. Under this approach, trades executed during the final 30 minutes of continuous trading and those conducted during CAS would both contribute to the settlement calculation.
The second option would use the final 30 minutes of continuous trading alone, at least temporarily. This would separate derivatives settlement from the new auction mechanism for a defined period.
The two options represent different regulatory philosophies.
The blended model would attempt to integrate CAS into the broader settlement process. It would preserve the role of the auction while reducing the influence of a potentially sharp price movement concentrated within the auction.
The alternative would prioritize stability by temporarily returning to a familiar settlement approach.
SEBI is also proposing changes to the closing process itself.
The post-closing auction period could be shortened, while the display of certain indicative prices could be changed.
In particular, SEBI is considering removing the indicative index closing value during CAS. The intention is to avoid confusion between an indicative number and the final index level.
At the stock level, indicative equilibrium prices may continue to be displayed.
The regulator is also examining order cancellation rules. Limit orders placed more than 1% away from the reference price could face restrictions on cancellation. This is intended to strengthen the integrity of the auction process and discourage potentially disruptive order activity.
These proposals could have implications for a wide range of market participants.
Institutional investors may benefit from greater clarity around closing prices. Derivatives traders could gain more certainty about expiry settlement. Brokers and exchanges, meanwhile, may need to update systems and procedures to accommodate the revised framework.
Retail traders could also notice changes in the information available during the closing period and in the way final prices are established.
Importantly, SEBI has not proposed abandoning CAS altogether. Instead, the regulator is attempting to refine the mechanism based on the experience of its initial implementation.
This approach reflects the importance of maintaining confidence in India’s market infrastructure.
A modern securities market requires reliable price discovery. At the same time, price discovery must not create unnecessary instability, particularly during periods when derivatives contracts are reaching expiry.
SEBI has invited public comments on the proposals until October 3. The final framework will be shaped by the feedback received from exchanges, brokers, investors and other stakeholders.
The coming weeks will therefore be important for India’s financial markets.
The regulator’s ultimate goal is to create a closing process that is transparent, efficient and predictable. Whether that is achieved through a blended VWAP, temporary separation of derivatives settlement from CAS, or another modification will depend on the consultation process.
The CAS review is consequently more than a technical adjustment to market rules. It represents an important test of how India’s rapidly evolving equity and derivatives markets can balance innovation with stability.
If SEBI’s proposed changes succeed, the revised framework could reduce expiry-day uncertainty while preserving the benefits of auction-based price discovery. If further issues emerge, the regulator may need to continue refining the system as market participants adapt to the new structure.
