Booking.com still runs on the internal A/B testing framework its engineers wrote in Amsterdam in the mid-2000s, with no major rewrite since, and at any given moment it is running more than 1,000 live experiments on the same booking page you're looking at
Booking.com runs more than 1,000 concurrent experiments on its production booking flow through an in-house framework its Amsterdam engineers built in the late 2000s — a foundational piece of software that has been extended continuously but never rewritten. The case reveals how the most powerful systems in modern e-commerce are often the oldest.
