When Helen Lofthouse became boss of ASX Limited in 2022, the market operator had sunk five years and $250 million into plans to replace its 25-year-old CHESS clearing and settlement system with a distributed ledger, the same technology used by cryptocurrencies such as bitcoin and ethereum.
The ASX's board had approved the plans in 2016 after it was promoted by then-chief Elmer Funke Kupper, but after years of delay, the blockchain-based system was still not ready to go live.
"The key thing that I needed to do from the moment I stepped into the CEO seat was to have a look at the previous CHESS project," Ms Lofthouse told AAP on Wednesday.
"I had to make an incredibly tough decision that the platform wasn't going to be delivering.
"The challenge for these types of systems is that it's critical market infrastructure that serves the entirety of the Australian market, and we have to operate those to incredibly high standards."
The system needed to be scalable and operate every day at the right level of resilience, she said.
Pulling the plug on the project was an embarrassment, leading to a lawsuit and fines by the securities regulator, and fury from investors and trading firms that had invested millions on their own upgrades in order to work with the experimental technology.
The ASX eventually regrouped, developing a new replacement for CHESS - a system that still runs on the decades-old computer language COBOL.
Stage one went live on Monday, handling clearing services, which are the checking of a trade's details so the parties can exchange securities and money at settlement.
Ms Lofthouse said hundreds of people at the ASX and its partner, Tata Consultancy Services, had worked on the project, and the new system was tested in parallel with the old system for 12 weeks.
"You can imagine the buzz, with hundreds of people waiting with bated breath as the market opens," said Ms Lofthouse, who was there for the event.
"The system is just running very smoothly, and (there are) lots of celebrations, as you can imagine."
Those 3.6 million trades that occurred on Monday settled on Wednesday, with $9.7 billion in value changing hands without issue.
The new system can accommodate three times more volume than the current system, will be faster and is cloud-based, with Amazon Web Services the bourse's main partner.
The second stage, which will handle settlement activities, is targeted for delivery in 2029.
Ms Lofthouse is stepping down from the ASX in May after 10 years in senior roles with the ASX, including the past four years as its first female chief executive.
