OpenAI is preparing to confidentially file a draft of its IPO prospectus as soon as Friday, as the company gears up for what could be one of the largest public markets debuts in history, CNBC confirmed on Wednesday.The artificial intelligence company, which is valued at more than $850 billion by private investors, is working with banks including Goldman Sachs and Morgan Stanley to prepare to file in the coming days or weeks, according to a source familiar with the matter who asked not to be name...