ChatGPT maker OpenAI confidentially filed for a US initial public offering recently, the company said on Monday, joining rival Anthropic in a push toward the stock market as investors seek exposure to the artificial intelligence boom. OpenAI did not disclose the size or terms of the offering, and said a timeline has not yet been determined. “It may be a while because there are things we want to do that are likely easier as a private company,” it said in a statement. Reuters had reported that the AI giant is targeting a valuation of up to $1 trillion in a stock market debut that could come as early as September. At that valuation, OpenAI would set the stage for a trio of trillion-dollar-valuation companies ⁠debuting rapidly, ​which together are seen as the most consequential test of investor appetite for high-growth technology stocks in the last 10 years. Elon Musk’s SpaceX was the first off the block, filing for an IPO that would rank as the largest in history if completed, with the company pursuing a …