Modifications in pre-open session in the equity segment, starting September 7, 2026

General
1

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.

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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

  1. Market orders match against other market orders first, on time priority.
  2. Any market orders left over get matched against limit orders, price-time priority.
  3. 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.

4 Likes
Is there any change in Pre market session?
3

What is sebi upto? They can’t even make sure CAS is working properly. Now hell bent on making more changes. This is becoming too much intervention day by day. Now what will be the benefit of doing above. I am sure sebi will have some grand logic for this as well. Better to completely leave the the market if this is how they will keep meddeling.

4

Hi nithin,

Is this also going live from next week?

Also you mention order matching priority is unchanged. But it is getting changed right. Right now i think limit order gets the priority.Attached the link below.

5

Yes, as of now, it will go live next week (Sept 07). Order preference is getting changed. Market orders are given priority.

2 Likes
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8

so basically, it’s just a timings change ?

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Ah, no.

Earlier, both market and limit orders could be placed, modified or cancelled until order entry closed randomly between 9:07 to 9:08 AM, and limit orders had priority during matching.

From Sept 7, market orders can only be placed, modified or cancelled in the first 5 mins, while limit orders can continue till order entry closes randomly between 9:08 to 9:10. Market orders get priority now during matching.

Further, Gold and Silver ETFs currently don’t participate in pre-open. This will be included from Sept 7.

2 Likes
10

is it truly random , fair and unknown to all, or is there some sort of manipulation possible in that ?

11

The closing time is decided by the exchange’s system, so it’s not something anyone can predict in advance.

The random timing is there to make sure no one can plan around it or influence it. Hence, there’s no way for anyone to control exactly when order entry will close.

2 Likes
12

@nithin_kumrr @KarthikAcharya

Could you please clarify the AMO process for ETFs on Zerodha except Gold and Silver EtF?

  1. Will Zerodha continue to allow AMO orders for ETFs under the same process, or is there any change effective from 7 September?
  2. If I place an ETF AMO order before market opening, until what time can I cancel or modify it?
  3. Will Zerodha send the ETF AMO order to the exchange at exactly 9:15 AM, or is it submitted to the exchange before 9:15 AM?
  4. If the order is sent at 9:15 AM, will I be able to cancel it before 9:15 AM, or does the cancellation window close earlier?

I would appreciate clarification on the exact timeline, particularly for ETF AMO orders.

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For Gold and silver Etfs you can place AMO till 8 58 AM. For other ETFs, it shall be till 9 11 AM.

For ETFs other than Gold and Silver, orders can be modified until 9:11 AM.

For Gold and Silver ETFs, market orders can be modified until 9:05 AM, while limit orders can be modified until 9:08 AM.

Gold and Silver ETFs will follow the pre market session timings that is at 9 AM, while all other ETFs orders will start from 9:15 AM.

Cancellation is allowed until 9:11 AM for ETFs other than Gold and Silver ETFs, as mentioned above.

1 Like
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@nithin_kumrr

I think zerodha systems were not updated. The system stopped accepting orders post 9:08.
This is what happens when regulator meddles with the framework continously.

Can zerodha team please confirm what happened ? Please update the system correctly.

15

You can DM your id and the issue with screenshot. We will check.

16

userid : DV4084
Preopen order placed via API is getting rejected after 09:08 AM, but today pre-open closed around 09:09:50 AM…
The enpoint replied “The order collection period in pre-open session is over. Regular trading will commence from 9:15 AM…” while placing order after 09:08AM

17

Pre-Open limit orders started getting rejected after ~09:08 (“order collection period is over”), even though NSE pre-open was still open till ~09:09:51. Cancels were fine. Has Zerodha updated the OMS for the new pre-open window?

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The issue happened for me as well while placing order using api.

@Matti @Ragavendran_M

Can you please check.

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@nivas_k +

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As exchange says before 9.10AM any time order match will happen within last 2 min, orders would have blocked after 9.08 AM. Kindly check this tomorrow and it should be fine.

2 Likes
21

Why would order block after 9:08 am. The pre-open closed around 09:09:50 AM. So anytime before that orders should have gone through.

@siva @nivas_k @Ragavendran_M

Can you please check if the issue only occurred for api users and system variables needs to be updated at your end?

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We have reviewed the flow and ensured it is aligned with the expected behavior. Please check this tomorrow, and the orders should be processed as expected.