I think the op was saying that you already owned the stock - that now becomes worth 1,000,000 and presumably would have paid income tax for the FY when you vested.

You surly don't pay income tax on the gain of already owned stock but CGT.

Back in the day 2000's I did own stock that was worth over 1,000,000 certainly wouldn't have had to have paid income tax if we had been bought out at point - but that was in the UK

This subthread is about selling at point of vesting. Unless you are a founder with a 86(b) election, when you vest it is income.