Kayvon was a huge driving force behind all the interesting product efforts of the last few years: Spaces, Fleets, topics, etc. Twitter went from not iterating on product (remember when Twitter's only change in several years was to change the star to a heart?) to starting to take some shots. Behind the scenes he was often pushing against significant headwinds that resisted product change (not the least of which was the internal 'sacred cow' that all things must be built with Scala and only run inside Twitter's on-prem datacenters).