Ambiance was different compared to today: https://twitter.com/TikTokInvestors/status/16151898803212410...
Whatsapp had 35 engineers for 450M users at the time of its acquisition by FB (2014). It had 50 engineers for 900M users (2015).
https://www.wired.com/2015/09/whatsapp-serves-900-million-us...