The default post-termination exercise window is 90 days. If you leave (whether voluntarily or not) and don't exercise within that window, your unexercised options expire. At a high-growth company, this is often a six-figure decision.
Why 90 days
It's a legal requirement to maintain ISO tax status. The IRS requires that ISOs be exercised within 90 days of departure to qualify for ISO treatment. Companies use 90 days as the default for both ISO and NSO grants for consistency.
Extended exercise windows
Companies like Pinterest, Quora, Coinbase have offered 7–10 year exercise windows for years. The trend is spreading: Anthropic, Stripe, others have moved to 5+ year windows for departing employees.
An extended-window exercise converts the option from ISO to NSO at the time of exercise (any exercise beyond 90 days loses ISO status). You'll pay ordinary income tax on the spread instead of AMT preference — usually worse, but at least you don't lose the option.
When you negotiate your offer, ask for an extended exercise window in writing. It costs the company nothing today but can save you tens of thousands later. Most companies will agree if asked specifically; few will offer it spontaneously.