When Ant Group goes public later this year, the Chinese financial-technology behemoth will likely earn a stratospheric market valuation that would place it at the top of companies listing globally for the first time.

In the coming days, the company controlled by billionaire Jack Ma could shed light on what has been a closely guarded secret for years: how it actually makes money. Ant, which is preparing for blockbuster share sales in Hong Kong and Shanghai, is planning to file its listing documents with exchanges in both cities this week, according to people familiar with the matter, kicking off a process that could have the company go public by October.