Having (almost) all of your net worth in one company is not a good general investment advice, especially if you are not already independently wealthy. That being said, there were people who got immensely rich by doing just that and keeping a lot of their net worth inside one company for a long time. In general though, one should rather try to diversify broadly.

I suppose this round is mainly present to retain those employees who want to buy houses from their shares, as in big tech they would be getting, after vesting, highly liquid RSUs. The fact that the company leadership makes an entire round just for them shows what immense bargaining power they have.

Depends if you’re already rich enough that you don’t care about the outcome, however rich that is.

OpenAI is aiming far higher than 800 billion, and with no public offering, there’s no other way to be part of it.

Sell half your shares if possible?

You should never invest in your employer anyway, at least not if you can't hedge.

I think evaluation grew like 4 times in a year, it is a good deal.