It was, however, optional and hidden behind a "For You" tab. The default homepage experience was still the chronological activity of users you follow.

This appears to have changed (unless I'm a part of some horrible A/B test), and the new algorithmic feed is now the only option. There are options to filter noise out of the feed (announcements, releases, sponsors, "recommendations", etc), but the resulting feed is completely useless in that it doesn't include the stars / repos of people I explicitly follow. If it were a strict superset of functionality of the old "following" tab and I could disable all of the noise, then I'd be fine with it, but as things stand, none of the old events appear in my feed.

This is a really useful, core feature of GitHub imho. I've spent years curating a close group of developer experts who I trust and frequently use GitHub's "following" feed in order to stay up-to-date with their work.

Please GitHub, make the algorithmic feed optional as it has been since it's introduction back in March.

Note that this change doesn't seem to appear in GitHub's official changelog (https://github.blog/changelog/), so hopefully it's just an ill-advised A/B test, but I'd be pretty upset if it wasn't.