Can I use page says that Chrome supports brotli for some time now. I would think that the Accept-Encoding string would be like this:

Accept-Encoding:gzip, deflate, sdch, br

But I checked on a request to StackOverflow e.g. and it does not contain brotli:

Accept-Encoding:gzip, deflate, sdch

I suppose most web servers won't really return you brotli if it's not in Accept-Encoding, so it's kind of partially supported only it seems.

Is it going to be added later or there is some trick I don't know of?

Brotli only works over HTTPS

There are many blog posts about this if you Google it. Here's one:

https://samsaffron.com/archive/2016/06/15/the-current-state-of-brotli-compression

Brotli is HTTPS only

If you visit a site over HTTP your browser will not accept the br encoding. The reasoning for this is documented at the end of the chromium issue.

The Chromium issue linked is here:

https://bugs.chromium.org/p/chromium/issues/detail?id=452335

StackOverflow can be accessed on a non-HTTPS connection

Make sure you are going to https://stackoverflow.com instead of http://stackoverflow.com

EDIT: StackOverflow can no longer be accessed on non HTTPS connection.