SEBI Proposes Major Overhaul of Closing Auction Session and Expiry Settlements to Curb Market Volatility — September 14, 2026

Barely six weeks after introducing the Closing Auction Session (CAS) for equity cash and derivatives segments, the Securities and Exchange Board of India (SEBI) has initiated a comprehensive review of the mechanism following market-wide friction and elevated volatility. Introduced on August 3, 2026, across roughly 200 stocks in the futures and options (F&O) segment, the closing auction framework was intended to bring Indian markets in line with global best practices by replacing the 30-minute volume-weighted average price (VWAP) calculation with an equilibrium price discovery session.

However, the transition triggered sharp price swings in benchmark indices—exemplified by intraday swings exceeding 1,000 points on BSE Sensex expiry days—and sparked allegations of order-book gaming by algorithmic trading desks. In response, SEBI has published a detailed consultation paper proposing key structural amendments and has invited stakeholder comments through October 3, 2026.

Two Options for Expiry-Day Derivatives Settlement

Under the current setup, the closing price discovered during CAS directly feeds into the final settlement price of expiring index and single-stock derivatives contracts, exposing options traders to sudden shocks during the final matching process. SEBI has proposed two specific alternatives to address this risk:

• Option 1 (Blended VWAP): The expiry settlement price would be calculated based on actual traded values across both the final 30 minutes of the Continuous Trading Session (CTS) and the 10-minute CAS. Rather than applying an arbitrary fixed ratio, the weighting would dynamically reflect the actual turnover recorded in each window.
• Option 2 (Return to CTS VWAP): The regulator would temporarily decouple derivative settlement from the closing auction, calculating expiry settlement prices exclusively from the final 30 minutes of continuous trading. CAS would continue to discover the cash market closing price for stocks, with a possible shift to a blended calculation considered after at least one year.

Realigning Market Timings and Trading Windows

To minimize disconnects between the cash and derivatives segments, SEBI has also suggested two alternative timing structures, aiming to compress transition buffers and avoid prolonged post-auction uncertainty:

• Option A (Extended Cash Trading): Normal continuous trading for all equities would continue until 3:30 PM. Following a swift transition of roughly one minute, CAS for F&O stocks would run from 3:31 PM to 3:40 PM, with derivatives trading concluding at 3:45 PM.
• Option B (Earlier CAS Completion): Continuous trading in CAS-eligible stocks would conclude at 3:15 PM, while non-CAS cash equities trade until 3:30 PM. CAS would operate between 3:15 PM and 3:25 PM, allowing derivatives trading to wrap up at the traditional closing time of 3:30 PM.

In both scenarios, SEBI proposes trimming the exchange buffer between continuous trading and CAS from five minutes to under one minute, while cutting the post-auction derivatives window from 10 minutes to five minutes.

Clamping Down on Spoofing and Order Cancellations

A major point of concern for SEBI has been the misuse of indicative price discovery during the uncrossing window. The regulator highlighted enforcement findings where large, non-genuine orders placed during CAS were cancelled just before matching, distorting indicative index levels to benefit opposing positions in expiring options contracts.

To eliminate this manipulative behavior, SEBI plans to introduce strict order cancellation rules during CAS, limiting the ability of participants to withdraw large blocks once entered.

While SEBI Chairman Tuhin Kanta Pandey affirmed that the closing auction mechanism itself is a permanent fixture necessary for handling massive institutional rebalancing flows—such as those during MSCI index rebalancings—the swift regulatory pivot highlights SEBI’s intent to curb unintended retail fallout and derivatives market manipulation.

Tags: SEBI NSE BSE Nifty 50 BSE Sensex Closing Auction Session