Is the web browser performance rule “only 2 requests in parallel per hostname” still correct?

Question

In his book \"High Performance Websites\" Steve Souders wrote (2007) that browsers limit parallel requests to a domain/hostname to two at a time. Is this still valid today?<

Answer 1

The HTTP/1.1 spec suggests a cap of 2 simultaneous requests per host (With HTTP/1.0 a figure of 4 was more common).

It would be wise to assume that the client might not be able to have more than 2 simultaneous requests open at once.