At a liquidity event such as an M&A, unexercised stock option grants are typically cashed out for a value equal to the spread between the exercise price and the liquidity price per share net to common stockholders.  When the company executes such a payout, it is considered a compensation event and subject to payroll taxes. This includes both the employee’s medicare and social security taxes as well as the employer’s matching

If you hold ISOs and your company is acquired, then you may trigger the 100K Limit Rule if your option agreement has an acceleration feature. Suddenly vesting all or more of your unvested options will increase the total number of options you vest for the year. Although your original grant was designed to stay under the 100K Limit, you may suddenly exceed it unintentionally.  As a result, some of your ISOs will be [epq-quote align="alig