Linux Development Numbers

15,600 developers since 2005 "when the adoption of Git made detailed tracking possible"

https://www.linuxfoundation.org/blog/2017/10/2017-linux-kernel-report-highlights-developers-roles-accelerating-pace-change/

Annual

• 4300 developers per year, from 500 companies in 2017 - [1]
• The number of unpaid developers continues a slow decline - [2]