OpenAI files for a confidential IPO, leading to questions about challenges it will likely face regarding business structure and revenue.

The moves comes days ahead of SpaceX's IPO.

Claude-maker Anthropic filed to go public on June 1, while competitor SpaceX will debut on the Nasdaq on June 12.

OpenAI files confidential IPO paperwork with SEC, opening door to potential listing as AI race heats up with rivals like Anthropic and SpaceX.