Dont all private companies require approval for secondary sales, which I assume are not ever approved?
Typically. I’d be shocked if OpenAI let employees sell their options like this without requiring approval
They don't but you effectively do it under the table
Do they sell at full value?
How do you define value without an IPO?
Whatever they sell them for is the value.
They do, but you sell forward contracts instead. This is perfectly legal, and the approach I've seen. There are a few companies, and even funds that will engage in this, in an effort to attain future upside.