Booking.com: Homepage — 3 Search Bars Challenging The Fewer Form Fields Pattern

I've been watching this Booking experiment closely ever since sharing a very similar concept some months ago. Their homepage was openly challenged with the UI hypothesis of exposing a "room quantity" field right in the search bar (instead of hiding it in a pulldown menu). And their team took the initiative to run a test. Based on the observed outcome and roll out decision it turns out that the UI concept was better than their control.