Preload headers DO NOT function "effectively the same" the same as HTTP/2 Push. Yes they have similar outcomes, no that does mean they function the same. They a

Preload headers DO NOT function "effectively the same" the same as HTTP/2 Push. Yes they have similar outcomes, no that does mean they function the same. They are related, but are not actually that similar except in the most trivial ways like using the word "Preload" - HTTP/2 Push: When the server thinks a client needs the resource, it pushes it into the client proactively, avoiding one round trip for the resource. The goal is to improve latency by sending the resource actively, independently of any DOM->render pipeline that would trigger the fetch. - Preload header: When the client requests a resource, the server delivers the page body, but it also tells it what it can load in parallel before parsing or JS eval. The goal is to improve latency by moving up the "fetch" stage, before the parse->DOM->render pipeline that would trigger the fetch. And beyond those two, over the past few years a new kid has appeared on the block: - 301 Early Hints: When the client requests a resource, the server sends a Preload hint telling it what to load before it even finishes generating the response. A 301 is delivered before the body is fully delivered, before even the first byte. The goal is to improve latency even further by moving the fetch stage up even earlier in the pipeline. Yes, they attack the same soft spot, but mechanically there is a VERY big difference between server-initialization and client-initialization, and between along-with-body and before-first-byte. (Obviously, 301s and Preloads are closer than anything.) Ignore the security stuff. The simplest reason HTTP/2 Push isn't so great is because it's not very good at accomplishing its goal. This is because browsers employ an ancient technique, originally written in hieroglyphs, called "caching", which means that the browser just won't request a resource if it already has it. A cache hit is the ultimate reduction in latency. But only the client browser knows what is in its cache, the server has no idea. With Push, you run a very real possibility of sending resources that aren't needed, overall losing efficiency. With 301s/preloads, you at worst receive a few wasted bytes from the useless headers. It's both much easier to get right, and much less costly if you get it wrong. It's also complicated to implement on top of all the other stuff. Preloads and 301s are vastly simpler and much more targeted additions to the HTTP stack, and HTTP is only useful insofar as implementations are compatible. So 301s/Preload are significantly easier to support and achieve much of the same purported benefits.