Comment by lateforwork

If you quit at age 55 or later and you have been with Microsoft for 15 years your stock continues to vest. That has always been the case.

This "buyout" appears to extend that benefit to employees who are >= 50 and have been with the company for 20 years. (Or any other combination that adds up to 70, for example you are 46 and have been with the company for 24 years).