Okay, so that requires the company to be sold for at least $1B, the employees collectively own 100% of the company, and the stock is evenly distributed. Given the investor's share and uneven distribution among employees, for there to be 1000 millionaires, the company would have to sell for at the very least $5B (probably much more). There are only a handful of companies that have sold at that level, certainly not common.
Only one I can think of is Uber where there could’ve been that many employees with significant equity, but that is really a generational company. Thinking of the ones that reach peak value in the low billions.
AFAIK engineers were getting around 12K RSUs pre IPO, maybe 20K for senior ones, which at today’s valuation is not even close to a million.
That's just one company.