The exchanges have released circulars today revising the pre-open call auction session for both the equity and equity derivatives segments. These changes are in line with SEBI’s January 16, 2026 circular and will come into effect from Monday, September 7, 2026.
Before we get into the changes, let’s understand the pre-open session. It is a short window before regular market trading begins. It helps discover a fair opening price and reduce volatility at the open. During the order entry period, buy and sell orders are collected, after which the exchange determines the equilibrium price, the price at which the maximum quantity can be matched. This equilibrium price becomes the opening price for the day.
Here’s the breakdown of the changes effective from Monday, September 7, 2026.
The pre-open session still runs from 9:00 AM to 9:15 AM. The only change is how those 15 minutes are split.
Also, 9:05 - 9:10 am windows will have a random stoppage during their last two minutes.
This aligns pre-open with the Closing Auction Session (CAS) framework
SEBI’s January 16, 2026 circular introduced CAS and directed exchanges to align the pre-open framework with the same design, the two-leg order entry, the random stoppage, and the market order cutoff.
Order matching priority remains unchanged
- Market orders match against other market orders first, on time priority.
- Any market orders left over get matched against limit orders, price-time priority.
- Remaining limit orders get matched against other limit orders, price-time priority.
Order type rules remain unchanged
- Limit and market orders placed with any of the three validity types, EOS (End of Session), EOD (End of Day), and IOC (Immediate or Cancel), are considered while determining the equilibrium price.
- Full quantity has to be shown, no disclosed quantity orders.
- No stop loss orders.
- Algo orders allowed, limit throughout, market order only in the first 5 minutes.
Indicative price will be available during pre-open
You’ll continue to see the price shown with the indicative price as orders come in, and the market depth showing the best bids and offers with their quantities.
Closing reference price now shown for Stock futures
Stock futures will now also get a closing reference price, shown between 3:15 pm and 3:20 pm, at the same time as CAS-eligible securities in the equity segment.
No new API version is required for trading members
This part is only for brokers and their tech teams. No new API version is needed, the existing versions of Enhanced Trading Interface and the exchange’s market data feeds that went live for CAS will work for pre-open too. Your broker handles all of this at their end.