Coke Zero launched in New Zealand and Australia in 2006 and was an instant success, but in some markets it is no longer available.
Coke No Sugar launched in June last year as part of Coca-Cola's commitment to reducing sugar, with the company signing up to an industry-wide pledge to reduce sugar by 20 per cent across its portfolio of sales by 2025.
Coke No Sugar was developed to taste more like Coca-Cola Classic but without the sugar.
"It is no surprise that people are preferring it over Coke Zero — just as we have seen where we have launched this new recipe around the world," Austin told news.com.au.
Austin said Coke No Sugar had eclipsed expectations since its launch.
"We can reveal that over 600,000 Kiwis have enjoyed a Coke No Sugar since launch and many of them are now regular drinkers," the Coca-Cola New Zealand spokeswoman said.
About 3.5 million Australians have also purchased a Coke No Sugar since the drink launched.
"We a seeing that the rapid growth of Coke No Sugar is helping to expand the low and no sugar drinks category overall," Austin said.
The phase-out of Coke Zero in Australia is due to be complete by September.
- Additional reporting from news.com.au