SEBI: CAS A Step Towards Strengthening Market Price Discovery Mechanism
SEBI highlights CAS as a step toward stronger price discovery.
The Securities and Exchange Board of India (SEBI) has described the new Closing Auction Session (CAS) framework as a significant step towards strengthening India's price discovery mechanism. In its latest annual report, the capital markets regulator said the revamped system is aimed at making closing prices in the Indian stock market more reliable and improving consistency with global market practices.
SEBI's assessment comes days after the new CAS framework was implemented in the domestic equity market on August 3, 2026. Since its introduction, the mechanism has been accompanied by sharp price movements during the final minutes of trading, prompting concerns among some market participants. Traders have also pointed to differences between index closing levels and futures prices following the new process.
According to SEBI, the earlier reliance on the volume weighted average price (VWAP) methodology could contribute to intraday price movements and volatility, particularly during periods of index rebalancing. Large institutional transactions could also create challenges for the market in absorbing significant flows in real time. The regulator said the CAS was introduced to address these concerns and bring India's closing-price mechanism closer to international practices followed by major exchanges.
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Under the earlier VWAP system, the closing price was determined by averaging trades executed during the final 30 minutes of the continuous trading session in the cash market. The CAS instead brings buy and sell orders together through a single auction, allowing market participants to interact simultaneously. The mechanism is designed to establish an equilibrium closing price based on the maximum matching of demand and supply.
SEBI has argued that the auction-based process can reduce price disruption and improve execution certainty, particularly during periods of heavy trading activity. The regulator said the framework is intended to produce a more stable and reliable closing price while strengthening the overall price discovery process in the Indian equity market.
The new CAS framework came into force on August 3, with the auction session scheduled between 3:15 pm and 3:35 pm. During the initial phase, the system applies to stocks in the equity cash segment that have derivative contracts available. For securities outside the scope of the new framework, closing prices will continue to be determined using the existing 30-minute VWAP methodology.
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