They're known as the "Royals" and "the chosen ones" — the select few invited to be in New York on Thursday morning to ring the bells celebrating the opening of the stock exchange and Australian tech darling Atlassian's massive IPO.

About 40 Atlassian employees — many of whom were hand-picked by co-founders Mike Cannon-Brookes and Scott Farquhar in the company's early years — celebrated overnight as they became multi-millionaires and Atlassian became a company with a market cap of $US5.74 billion ($7.9 billion).

By the end of Thursday's trading in the US, however, more than just those 40 became millionaires. Former Atlassian employees say more than 100 staff are now either millionaires or multi-millionaires.