A billionaire on paper, mostly in Twitter stock (which means he has lost a lot of that paper wealth lately) and in Square which hasn't had an IPO yet. It's not a giant move, but a $900k insider purchase is fairly big.
Jack has probably half a billion dollars of non square, non twitter assets. Hell, merely post ipo he's sold almost 20m shares of twitter -- even at a stock price of just $30, that's $600e6 before taxes. And he's certainly had the ability to take cash before ipo in both twitter and square.
He started out with 22,203,018 shares and before the latest purchase had 21,888,416 shares, for a total of 314,602 sold shares (or a mere 1.4%). If anything that's a surprisingly little amount of shares sold considering it is the bulk of his net worth. Note that he's a billionaire if you count the equity in Square, his Twitter holdings come out to $645M (counting a cool $54 net gain on his TWTR holdings today!).
And why would he have to sell shares during the ipo? As far as I understand, he should have had virtually no expenses, assuming he (as all founders should) did an 83b election early on.
