# SEBI updates CAS rules for F&O traders

> SEBI's new CAS rules from Dec 7 could cut expiry-day volatility and boost brokers.
- Title: SEBI updates CAS rules for F&O traders · Financialexpress
- Summary: SEBI's new CAS rules from Dec 7 could cut expiry-day volatility and boost brokers. SEBI's revised Closing Auction Session rules, effective Dec 7, 2026, aim…
- Keywords: sebi, cas, f&o traders, brokers, groww, sebi rules, expiry day volatility, closing auction session, business, money, news, updates
- Source: Financialexpress — https://financialexpress.com/market/sebi-overhauls-cas-rules-from-dec-7-what-changed-for-fampo-traders-amp-brokers-4362852
- Author: Oliviya Kunjumon
- Published: 2026-10-16T06:27:48+00:00
- Read time: 1 min
- Topics: sebi, cas, f&o traders, brokers, groww, sebi rules, expiry day volatility, closing auction session, business, money, news
## SEBI revises CAS rules
SEBI updates Closing Auction Session rules to reduce expiry-day volatility and benefit brokers more than exchanges.

> cas: sebi removes uncertainty; bigger +ve for brokers vs exchanges
## Key changes effective Dec 7
SEBI's revised framework takes effect on December 7, 2026, including new reference price calculations and shorter auction timing.
## How brokers benefit
Jefferies sees brokers gaining from reduced volatility as order activity returns to pre-CAS levels.
## New reference price method
SEBI uses volume-weighted average price of constituent stocks during continuous trading for index derivatives.
## Auction timing adjustments
CAS timings shortened to 10 minutes with reference price calculation from 3:30 pm to 3:31 pm.
## Brokers vs exchanges impact
Brokers may benefit more than exchanges as order activity remains below pre-CAS levels.
## What investors should watch
Lower expiry-day volatility could improve broker activity, but actual impact depends on trading behavior.
## Key takeaway

SEBI's revised Closing Auction Session rules, effective Dec 7, 2026, aim to reduce expiry-day volatility and benefit brokers more than exchanges.