I've seen replies about how this is a "simple library swap" and so doesn't deserve the attention it recognition it has received. As some who works at Google but not anywhere remotely near this project, but with experience in similar projects, I'd like to shed some light on why this isn't a simple library swap, and seems from far away to have been both a tremendous accomplishment and a wonderful learning experience.
First off, there is no such thing as a library swap at Google. Our codebase is quite large. Like shockingly overwhelmingly large. Executing a change like this is almost certainly not a case of "swapping out one configuration line for another." It requires writing new code, testing it appropriately, updating any integration tests, updating documentation, etc. But the real fun starts when you're done coding...
There's the issue of frontend and backend. Serving Brotli-compressed data is great, but what if you're app doesn't support it? If you're lucky, this will be handled by the underlying network layer but then you have to deal with...
Rollout. I don't know how many servers are dedicated to app updates, but I imagine it's a lot. I also imagine they're distributed geographically, across regions and probably even continents. Getting all those servers to support new features is a delicate, time consuming process where any misstep will result in users noticing. It's not coding, but that's why it's called "software engineering" and not "coding engineering." But then once you're servers are all up and running you have to deal with...
Versioning. Updating backend servers is bad enough, but at least you control them. What about that zoo of Android versions out in the wild? How do you ensure they all support this changes? Short answer: you don't. You design a strategy that will allow the rollout to happen gradually over a period of time, and closely monitor it to make sure nothing unintended is happening.
Then how do you turn down the old feature? When do you turn it down? You need to build and properly use instrumentation to determine the safest time to kill off the old feature. Or you could never kill it and commit to paying the cost in perpetuity. That's a design decision, and not a trivial one.
But, odds are you're not the only feature being rolled out. You have to anticipate/deal with potential interactions with other features, rollbacks of other people's work, etc.
I could go on, but I think I've already demonstrated why this is by no means a trivial accomplishment, even for a full time engineer. Add to this the fact that every intern has to race against the clock to get ramped up on their project, making something of this complexity and with this large an impact happen deserves applause.
I should add, I'm speaking as myself here and not representing Google in any way.