Thanks for the link, that clarifies things so much. I had been circling around the "non-statutory options" on page 11, like you would get without the 90 day exe

Thanks for the link, that clarifies things so much. I had been circling around the "non-statutory options" on page 11, like you would get without the 90 day exercise clause. In that case, the taxable event is vesting (assuming the options can have a determined FMV). I see that I was confused by thinking FMV exercise price was part of the requirement to have an ISO, but instead the IRS clarifies in the middle of page 13 that any valuation below FMV is taxable on exercise (if it's an ISO, and not a nonstatutory option)