10 years is becoming somewhat of popular number, but I'm curious if in any cases it's a full 10 years from leaving a company. That is, I have seen in the wild an options grant agreement that indeed specified 10 years from leaving the company but the agreement itself expires after 10 years.

Therefore, you can vest all your shares, for example in 4 years, and then leave the company. But under this agreement you apparently have only 6 years then to exercise.

I suspect the 10 year figure comes from the statute on ISOs, which says the options must be exercisable only within 10 years from the options grant. (I have no idea if this rule allows the ISOs to turn into NSOs like the rule about 3 months from leaving the company does)

Anyhow, I think it's important to get to the bottom of this, because a common understanding of the extended exercise window issue is, instead of getting the common 3 months [from leaving] to exercise, with an extended exercise window you get as long as 10 years, when that may not really ever be true (with a 1 year cliff, you'd only actually get max 9 years from leaving).

Andreessen Horowitz initially opposed the extending the post termination exercise period to 10 years, but about a month later, they came out in support of the extension to 10 years, in conjunction with back-end loaded stock vesting, transfer restrictions, and moving to RSUs as valuations materially increase.

Sam Altman of Ycombinator supports extending the post termination exercise period to 10 years, also in conjuction with back-end loaded stock vesting and transfer restrictions.

In this comment thread https://news.ycombinator.com/item?id=11607539 it's mentioned that Instacart has a 7-year exercise window. But i don't have any further citations to back that up.