The filing is private, so details such as number of shares being offered and their price are unknown, for now.

Elon Musk's SpaceX is gearing up for what's likely to be the largest IPO in history and it has implications for the Invesco QQQ ETF.

April 1 (Reuters) - Elon Musk's SpaceX has confidentially filed for its hotly anticipated U.S. initial public offering, a person familiar with the matter told Reuters on Wednesday, taking space exploration from a speculative venture to a mainstream investment theme.