Indian stock exchanges introduced a new Closing Auction Session (CAS) on Aug. 3, 2026 [1].
The shift alters how securities are priced at the end of the trading day. While the mechanism aims to increase market-closing efficiency, it creates divergent outcomes for different investment vehicles based on how they track assets.
Exchange-Traded Funds (ETFs) have seen immediate benefits from the CAS. The mechanism improves execution accuracy and reduces tracking error, allowing these funds to align more closely with their underlying indices. This reduction in error typically leads to more stable performance for ETF investors.
Arbitrage funds, however, face significant operational hurdles. These funds rely on the narrow price difference between the cash market and the futures market to generate returns. The new auction process has caused a wider divergence between these two closing prices, a gap that can lead to sudden, single-day jumps in Net Asset Value (NAV).
Bhavesh Jain, president and co-head of factor investing at Edelweiss Mutual Fund, said the CAS creates short-term valuation volatility for arbitrage funds. This volatility stems from the way the auction settles the final price of the day, which may not align with the futures contract's movement.
Because arbitrage funds seek low-risk returns through price discrepancies, the increased volatility in the closing window introduces a layer of unpredictability. The divergence between the cash and futures prices remains the primary challenge for managers attempting to maintain steady NAV growth under the new rules.
“The new auction process has caused a wider divergence between these two closing prices.”
The implementation of the Closing Auction Session represents a trade-off in market microstructure. While it professionalizes the closing price for passive instruments like ETFs, it disrupts the precise price-convergence required by arbitrage strategies. This may force arbitrage fund managers to adjust their hedging timings or risk profiles to mitigate the impact of single-day NAV swings.
