The last startup I worked at had a small flock of employees that hit the 4 year mark this year. Unfortunately, most of them didn't do any sort of early exercise

The last startup I worked at had a small flock of employees that hit the 4 year mark this year. Unfortunately, most of them didn't do any sort of early exercise so they paid taxes on the difference after they exercised. The only thing that saved a few of them is that the company offered a buyback program so they were able to flip some (all, in some cases) of their shares to cover the exercise and the taxes.