What is a
Closing Auction Session?
A closing auction is a commonly used trading mechanism which allows trades to be executed at the closing price. During a closing auction, market participants may input buy and sell orders, with the price that most volume can be traded at forming the closing price. All orders will then be executed at that price.
What securities are
covered under CAS?
The CAS is rolled out in two phases:
  • Phase 1, launched in July 2016, includes constituent stocks from the Hang Seng Composite LargeCap and MidCap Indices, H shares which have corresponding A shares listed on a Mainland exchange, and all ETFs.
  • In Phase 2, the list of CAS Securities is expanded to include constituent stocks from the Hang Seng Composite SmallCap Index.
What were the
changes to trading hours?
For the securities markets, the market closing time has been changed from 16:00 to a random closing of anytime between 16:08 and 16:10 for a normal trading day. It has been changed from 12:00 to a random closing of anytime between 12:08 and 12:10 for a half day trading.

For the derivatives market, the closing times of normal trading sessions for Stock Index Futures and Options, Currency Futures and Commodity Futures have been changed from 16:15 to 16:30 for a normal trading day and from 12:00 to 12:30 for a half trading day, except on the last trading day of the contracts. The opening time of After-Hours Futures Trading has been changed from 17:00 to 17:15.

In addition, trading hours on the last trading day, the final settlement price calculation algorithm and typhoon arrangements have also been changed accordingly.